Adaptive application of generalized sample offset

ABSTRACT

This disclosure relates to adaptive loop filtering (ALF) for cross-component sample offset (CCSO), local sample offset (LSO), and generalized sample offset (GSO). ALF uses reconstructed samples of a first color component as input (e.g., Y or Cb or Cr). At least one of the GSO, LSO, or CCSO is determined to be enabled for a frame based on a syntax value in a coded video stream. The coded video stream is decoded by applying the at least one of the GSO, the LSO, or the CCSO at a block level.

INCORPORATION BY REFERENCE

This application is based on and claims the benefit of priority to U.S.Provisional Application No. 63/280,503, filed on Nov. 17, 2021, entitled“ADAPTIVE APPLICATION OF GENERALIZED SAMPLE OFFSET,” and U.S.Provisional Application No. 63/289,139, filed on Dec. 13, 2021, entitled“ADAPTIVE APPLICATION OF GENERALIZED SAMPLE OFFSET,” the contents ofeach of which are herein incorporated by reference in their entirety.

TECHNICAL FIELD

This disclosure describes a set of advanced video coding technologies.More specifically, the disclosed technology involves cross-componentsample offset (CCSO), local sample offset (LSO), and generalized sampleoffset (GSO).

BACKGROUND

This background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing of thisapplication, are neither expressly nor impliedly admitted as prior artagainst the present disclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, with each picture having a spatialdimension of, for example, 1920×1080 luminance samples and associatedfull or subsampled chrominance samples. The series of pictures can havea fixed or variable picture rate (alternatively referred to as framerate) of, for example, 60 pictures per second or 60 frames per second.Uncompressed video has specific bitrate requirements for streaming ordata processing. For example, video with a pixel resolution of1920×1080, a frame rate of 60 frames/second, and a chroma sub samplingof 4:2:0 at 8 bit per pixel per color channel requires close to 1.5Gbit/s bandwidth. An hour of such video requires more than 600 GBytes ofstorage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the uncompressed input video signal, through compression.Compression can help reduce the aforementioned bandwidth and/or storagespace requirements, in some cases, by two orders of magnitude or more.Both lossless compression and lossy compression, as well as acombination thereof can be employed. Lossless compression refers totechniques where an exact copy of the original signal can bereconstructed from the compressed original signal via a decodingprocess. Lossy compression refers to coding/decoding process whereoriginal video information is not fully retained during coding and notfully recoverable during decoding. When using lossy compression, thereconstructed signal may not be identical to the original signal, butthe distortion between original and reconstructed signals is made smallenough to render the reconstructed signal useful for the intendedapplication albeit some information loss. In the case of video, lossycompression is widely employed in many applications. The amount oftolerable distortion depends on the application. For example, users ofcertain consumer video streaming applications may tolerate higherdistortion than users of cinematic or television broadcastingapplications. The compression ratio achievable by a particular codingalgorithm can be selected or adjusted to reflect various distortiontolerance: higher tolerable distortion generally allows for codingalgorithms that yield higher losses and higher compression ratios.

A video encoder and decoder can utilize techniques from several broadcategories and steps, including, for example, motion compensation,Fourier transform, quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, a picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be referred to as an intra picture. Intra pictures and theirderivatives such as independent decoder refresh pictures, can be used toreset the decoder state and can, therefore, be used as the first picturein a coded video bitstream and a video session, or as a still image. Thesamples of a block after intra prediction can then be subject to atransform into frequency domain, and the transform coefficients sogenerated can be quantized before entropy coding. Intra predictionrepresents a technique that minimizes sample values in the pre-transformdomain. In some cases, the smaller the DC value after a transform is,and the smaller the AC coefficients are, the fewer the bits that arerequired at a given quantization step size to represent the block afterentropy coding.

Traditional intra coding such as that known from, for example, MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt coding/decoding of blocks based on, for example, surroundingsample data and/or metadata that are obtained during the encoding and/ordecoding of spatially neighboring, and that precede in decoding orderthe blocks of data being intra coded or decoded. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction uses reference data only from the currentpicture under reconstruction and not from other reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques are available in a given video coding technology,the technique in use can be referred to as an intra prediction mode. Oneor more intra prediction modes may be provided in a particular codec. Incertain cases, modes can have submodes and/or may be associated withvarious parameters, and mode/submode information and intra codingparameters for blocks of video can be coded individually or collectivelyincluded in mode codewords. Which codeword to use for a given mode,submode, and/or parameter combination can have an impact in the codingefficiency gain through intra prediction, and so can the entropy codingtechnology used to translate the codewords into a bitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). Generally, for intra prediction, a predictor block can be formedusing neighboring sample values that have become available. For example,available values of particular set of neighboring samples along certaindirection and/or lines may be copied into the predictor block. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions specified in H.265's 33 possible intra predictordirections (corresponding to the 33 angular modes of the 35 intra modesspecified in H.265). The point where the arrows converge (101)represents the sample being predicted. The arrows represent thedirection from which neighboring samples are used to predict the sampleat 101. For example, arrow (102) indicates that sample (101) ispredicted from a neighboring sample or samples to the upper right, at a45 degree angle from the horizontal direction. Similarly, arrow (103)indicates that sample (101) is predicted from a neighboring sample orsamples to the lower left of sample (101), in a 22.5 degree angle fromthe horizontal direction.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are example referencesamples that follow a similar numbering scheme. A reference sample islabelled with an R, its Y position (e.g., row index) and X position(column index) relative to block (104). In both H.264 and H.265,prediction samples adjacently neighboring the block under reconstructionare used.

Intra picture prediction of block 104 may begin by copying referencesample values from the neighboring samples according to a signaledprediction direction. For example, assuming that the coded videobitstream includes signaling that, for this block 104, indicates aprediction direction of arrow (102)—that is, samples are predicted froma prediction sample or samples to the upper right, at a 45-degree anglefrom the horizontal direction. In such a case, samples S41, S32, S23,and S14 are predicted from the same reference sample R05. Sample S44 isthen predicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has continued to develop. In H.264 (year 2003), for example,nine different direction are available for intra prediction. Thatincreased to 33 in H.265 (year 2013), and JEM/VVC/BMS, at the time ofthis disclosure, can support up to 65 directions. Experimental studieshave been conducted to help identify the most suitable intra predictiondirections, and certain techniques in the entropy coding may be used toencode those most suitable directions in a small number of bits,accepting a certain bit penalty for directions. Further, the directionsthemselves can sometimes be predicted from neighboring directions usedin the intra prediction of the neighboring blocks that have beendecoded.

FIG. 1B shows a schematic (180) that depicts 65 intra predictiondirections according to JEM to illustrate the increasing number ofprediction directions in various encoding technologies developed overtime.

The manner for mapping of bits representing intra prediction directionsto the prediction directions in the coded video bitstream may vary fromvideo coding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingmost probable modes, and similar techniques. In all cases, however,there can be certain directions for intro prediction that arestatistically less likely to occur in video content than certain otherdirections. As the goal of video compression is the reduction ofredundancy, those less likely directions will, in a well-designed videocoding technology, may be represented by a larger number of bits thanmore likely directions.

Inter picture prediction, or inter prediction may be based on motioncompensation. In motion compensation, sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), may be used for a prediction of a newly reconstructedpicture or picture part (e.g., a block). In some cases, the referencepicture can be the same as the picture currently under reconstruction.MVs may have two dimensions X and Y, or three dimensions, with the thirddimension being an indication of the reference picture in use (akin to atime dimension).

In some video compression techniques, a current MV applicable to acertain area of sample data can be predicted from other MVs, for examplefrom those other MVs that are related to other areas of the sample datathat are spatially adjacent to the area under reconstruction and precedethe current MV in decoding order. Doing so can substantially reduce theoverall amount of data required for coding the MVs by relying onremoving redundancy in correlated MVs, thereby increasing compressionefficiency. MV prediction can work effectively, for example, becausewhen coding an input video signal derived from a camera (known asnatural video) there is a statistical likelihood that areas larger thanthe area to which a single MV is applicable move in a similar directionin the video sequence and, therefore, can in some cases be predictedusing a similar motion vector derived from MVs of neighboring area. Thatresults in the actual MV for a given area to be similar or identical tothe MV predicted from the surrounding MVs. Such an MV in turn may berepresented, after entropy coding, in a smaller number of bits than whatwould be used if the MV is coded directly rather than predicted from theneighboring MV(s). In some cases, MV prediction can be an example oflossless compression of a signal (namely: the MVs) derived from theoriginal signal (namely: the sample stream). In other cases, MVprediction itself can be lossy, for example because of rounding errorswhen calculating a predictor from several surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 specifies, described below is atechnique henceforth referred to as “spatial merge”.

Specifically, referring to FIG. 2 , a current block (201) comprisessamples that have been found by the encoder during the motion searchprocess to be predictable from a previous block of the same size thathas been spatially shifted. Instead of coding that MV directly, the MVcan be derived from metadata associated with one or more referencepictures, for example from the most recent (in decoding order) referencepicture, using the MV associated with either one of five surroundingsamples, denoted A0, A1, and B0, B1, B2 (202 through 206, respectively).In H.265, the MV prediction can use predictors from the same referencepicture that the neighboring block uses.

AOMedia Video 1 (AV1) is an open video coding format designed for videotransmissions over the Internet. It was developed as a successor to VP9by building on the codebase of VP9, and incorporating additionaltechniques. The AV1 bitstream specification includes a reference videocodec, such as the H.265 or High Efficiency Video Coding (HEVC) standardor Versatile Video Coding (VVC).

SUMMARY

Embodiments of the disclosure provide methods and apparatuses forcross-component sample offset (CCSO), local sample offset (LSO), andgeneralized sample offset (GSO). Adaptive loop filtering (ALF) usesreconstructed samples of a first color component as input (e.g., Y or Cbor Cr). For CCSO, the output is applied on a second color componentwhich is a different color component of the first color component. ForLSO, the output is applied on the first color component. For GSO, acombined ALF may be generalized for CCSO and LSO by considering a deltavalue between neighboring samples of a collocated (or current) sampleand also considering a level value of the collocated (or current)sample. At least one of the CCSO, the LSO, or the GSO may be enabled fora frame based on a syntax value included in a coded video stream.

In one embodiment, a method includes: receiving a coded video streamcomprising a syntax element indicating whether a sample offset filteringprocess is applied to a frame in the coded video stream at a blocklevel; determining that at least one of: a generalized sample offset(GSO), a local sample offset (LSO), or a cross component sample offset(CCSO) is enabled for the frame based on the syntax element being apredefined value; and decoding the coded video stream by applying the atleast one of the GSO, the LSO, or the CCSO at the block level.

In another embodiment, an apparatus for decoding a video stream includesa memory storing a plurality of instructions; and a processor configuredto execute the plurality of instructions, and upon execution of theplurality of instructions, is configured to: receive a coded videostream comprising a syntax element indicating whether a sample offsetfiltering process is applied to a frame in the coded video stream at ablock level; determine that at least one of: a generalized sample offset(GSO), a local sample offset (LSO), or a cross component sample offset(CCSO) is enabled for the frame at the block level based on the syntaxelement being a predefined value; and decode the coded video stream byapplication of the at least one of the GSO, the LSO, or the CCSO at theblock level.

In another embodiment, a non-transitory computer readable storage mediumstoring a plurality of instructions executable by a processor, whereinupon execution by the processor, the plurality of instructions isconfigured to cause the processor to: receive a coded video streamcomprising a syntax element indicating whether a sample offset filteringprocess is applied to a frame in the coded video stream at a blocklevel; determine that at least one of: a generalized sample offset(GSO), a local sample offset (LSO), or a cross component sample offset(CCSO) is enabled for the frame based on the syntax element being apredefined value; and decode the coded video stream by application ofthe at least one of the GSO, the LSO, or the CCSO at the block level.

In some other embodiments, a device for processing video information isdisclosed. The device may include a circuitry configured to perform anyone of the method implementations above.

Embodiments of the disclosure also provide non-transitorycomputer-readable mediums storing instructions which when executed by acomputer for video decoding and/or encoding cause the computer toperform the methods for video decoding and/or encoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A shows a schematic illustration of an exemplary subset of intraprediction directional modes.

FIG. 1B shows an illustration of exemplary intra prediction directions.

FIG. 2 shows a schematic illustration of a current block and itssurrounding spatial merge candidates for motion vector prediction in oneexample.

FIG. 3 shows a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an example embodiment.

FIG. 4 shows a schematic illustration of a simplified block diagram of acommunication system (400) in accordance with an example embodiment.

FIG. 5 shows a schematic illustration of a simplified block diagram of avideo decoder in accordance with an example embodiment.

FIG. 6 shows a schematic illustration of a simplified block diagram of avideo encoder in accordance with an example embodiment.

FIG. 7 shows a block diagram of a video encoder in accordance withanother example embodiment.

FIG. 8 shows a block diagram of a video decoder in accordance withanother example embodiment.

FIG. 9 shows a scheme of coding block partitioning according to exampleembodiments of the disclosure;

FIG. 10 shows another scheme of coding block partitioning according toexample embodiments of the disclosure;

FIG. 11 shows another scheme of coding block partitioning according toexample embodiments of the disclosure;

FIG. 12 shows an example partitioning of a base block into coding blocksaccording to an example partitioning scheme;

FIG. 13 shows an example ternary partitioning scheme;

FIG. 14 shows an example quadtree binary tree coding block partitioningscheme;

FIG. 15 shows a scheme for partitioning a coding block into multipletransform blocks and coding order of the transform blocks according toexample embodiments of the disclosure;

FIG. 16 shows another scheme for partitioning a coding block intomultiple transform blocks and coding order of the transform blockaccording to example embodiments of the disclosure;

FIG. 17 shows another scheme for partitioning a coding block intomultiple transform blocks according to example embodiments of thedisclosure;

FIG. 18 shows an example adaptive loop filter (ALF) shape;

FIG. 19 a shows subsampled positions in a Laplacian calculation for avertical gradient;

FIG. 19 b shows subsampled positions in a Laplacian calculation for ahorizontal gradient;

FIG. 19 c shows subsampled positions in a Laplacian calculation for adiagonal gradient;

FIG. 19 d shows subsampled positions in a Laplacian calculation foranother diagonal gradient;

FIG. 20 shows an example of modified block classification at virtualboundaries;

FIG. 21 shows an example of modified adaptive loop filtering for lumacomponent at virtual boundaries;

FIG. 22 shows an example of largest coding unit (LCU) aligned picturequadtree splitting;

FIG. 23 shows an example of quadtree split flags encoded in the z order;

FIG. 24 shows an example of cross-component adaptive loop filter(CC-ALF) placement;

FIG. 25 shows an example of a diamond shaped filter;

FIG. 26 shows an example location of chroma samples relative to lumasamples;

FIG. 27 shows an example of direction search;

FIG. 28 shows an example of subspace projection;

FIG. 29 shows an example of a filter support area;

FIG. 30 shows an example loop filter pipeline;

FIG. 31 shows example inputs of cross-component sample offset (CCSO);

FIG. 32 shows example filter shapes in cross-component sample offset(CCSO);

FIG. 33 shows example pixel patterns;

FIG. 34 shows a flow chart of a method according to an exampleembodiment of the disclosure;

FIG. 35 shows a flow chart of another method according to an exampleembodiment of the disclosure; and

FIG. 36 shows a schematic illustration of a computer system inaccordance with example embodiments of the disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

Throughout the specification and claims, terms may have nuanced meaningssuggested or implied in context beyond an explicitly stated meaning. Thephrase “in one embodiment” or “in some embodiments” as used herein doesnot necessarily refer to the same embodiment and the phrase “in anotherembodiment” or “in other embodiments” as used herein does notnecessarily refer to a different embodiment. Likewise, the phrase “inone implementation” or “in some implementations” as used herein does notnecessarily refer to the same implementation and the phrase “in anotherimplementation” or “in other implementations” as used herein does notnecessarily refer to a different implementation. It is intended, forexample, that claimed subject matter includes combinations of exemplaryembodiments/implementations in whole or in part.

In general, terminology may be understood at least in part from usage incontext. For example, terms, such as “and”, “or”, or “and/or,” as usedherein may include a variety of meanings that may depend at least inpart upon the context in which such terms are used. Typically, “or” ifused to associate a list, such as A, B or C, is intended to mean A, B,and C, here used in the inclusive sense, as well as A, B or C, here usedin the exclusive sense. In addition, the term “one or more” or “at leastone” as used herein, depending at least in part upon context, may beused to describe any feature, structure, or characteristic in a singularsense or may be used to describe combinations of features, structures orcharacteristics in a plural sense. Similarly, terms, such as “a”, “an”,or “the”, again, may be understood to convey a singular usage or toconvey a plural usage, depending at least in part upon context. Inaddition, the term “based on” or “determined by” may be understood asnot necessarily intended to convey an exclusive set of factors and may,instead, allow for existence of additional factors not necessarilyexpressly described, again, depending at least in part on context.

FIG. 3 illustrates a simplified block diagram of a communication system(300) according to an embodiment of the present disclosure. Thecommunication system (300) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (350). Forexample, the communication system (300) includes a first pair ofterminal devices (310) and (320) interconnected via the network (350).In the example of FIG. 3 , the first pair of terminal devices (310) and(320) may perform unidirectional transmission of data. For example, theterminal device (310) may code video data (e.g., of a stream of videopictures that are captured by the terminal device (310)) fortransmission to the other terminal device (320) via the network (350).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (320) may receive the codedvideo data from the network (350), decode the coded video data torecover the video pictures and display the video pictures according tothe recovered video data. Unidirectional data transmission may beimplemented in media serving applications and the like.

In another example, the communication system (300) includes a secondpair of terminal devices (330) and (340) that perform bidirectionaltransmission of coded video data that may be implemented, for example,during a videoconferencing application. For bidirectional transmissionof data, in an example, each terminal device of the terminal devices(330) and (340) may code video data (e.g., of a stream of video picturesthat are captured by the terminal device) for transmission to the otherterminal device of the terminal devices (330) and (340) via the network(350). Each terminal device of the terminal devices (330) and (340) alsomay receive the coded video data transmitted by the other terminaldevice of the terminal devices (330) and (340), and may decode the codedvideo data to recover the video pictures and may display the videopictures at an accessible display device according to the recoveredvideo data.

In the example of FIG. 3 , the terminal devices (310), (320), (330) and(340) may be implemented as servers, personal computers and smart phonesbut the applicability of the underlying principles of the presentdisclosure may not be so limited. Embodiments of the present disclosuremay be implemented in desktop computers, laptop computers, tabletcomputers, media players, wearable computers, dedicated videoconferencing equipment, and/or the like. The network (350) representsany number or types of networks that convey coded video data among theterminal devices (310), (320), (330) and (340), including for examplewireline (wired) and/or wireless communication networks. Thecommunication network (350) may exchange data in circuit-switched,packet-switched, and/or other types of channels. Representative networksinclude telecommunications networks, local area networks, wide areanetworks and/or the Internet. For the purposes of the presentdiscussion, the architecture and topology of the network (350) may beimmaterial to the operation of the present disclosure unless explicitlyexplained herein.

FIG. 4 illustrates, as an example for an application for the disclosedsubject matter, a placement of a video encoder and a video decoder in avideo streaming environment. The disclosed subject matter may be equallyapplicable to other video applications, including, for example, videoconferencing, digital TV broadcasting, gaming, virtual reality, storageof compressed video on digital media including CD, DVD, memory stick andthe like, and so on.

A video streaming system may include a video capture subsystem (413)that can include a video source (401), e.g., a digital camera, forcreating a stream of video pictures or images (402) that areuncompressed. In an example, the stream of video pictures (402) includessamples that are recorded by a digital camera of the video source 401.The stream of video pictures (402), depicted as a bold line to emphasizea high data volume when compared to encoded video data (404) (or codedvideo bitstreams), can be processed by an electronic device (420) thatincludes a video encoder (403) coupled to the video source (401). Thevideo encoder (403) can include hardware, software, or a combinationthereof to enable or implement aspects of the disclosed subject matteras described in more detail below. The encoded video data (404) (orencoded video bitstream (404)), depicted as a thin line to emphasize alower data volume when compared to the stream of uncompressed videopictures (402), can be stored on a streaming server (405) for future useor directly to downstream video devices (not shown). One or morestreaming client subsystems, such as client subsystems (406) and (408)in FIG. 4 can access the streaming server (405) to retrieve copies (407)and (409) of the encoded video data (404). A client subsystem (406) caninclude a video decoder (410), for example, in an electronic device(430). The video decoder (410) decodes the incoming copy (407) of theencoded video data and creates an outgoing stream of video pictures(411) that are uncompressed and that can be rendered on a display (412)(e.g., a display screen) or other rendering devices (not depicted). Thevideo decoder 410 may be configured to perform some or all of thevarious functions described in this disclosure. In some streamingsystems, the encoded video data (404), (407), and (409) (e.g., videobitstreams) can be encoded according to certain video coding/compressionstandards. Examples of those standards include ITU-T RecommendationH.265. In an example, a video coding standard under development isinformally known as Versatile Video Coding (VVC). The disclosed subjectmatter may be used in the context of VVC, and other video codingstandards.

It is noted that the electronic devices (420) and (430) can includeother components (not shown). For example, the electronic device (420)can include a video decoder (not shown) and the electronic device (430)can include a video encoder (not shown) as well.

FIG. 5 shows a block diagram of a video decoder (510) according to anyembodiment of the present disclosure below. The video decoder (510) canbe included in an electronic device (530). The electronic device (530)can include a receiver (531) (e.g., receiving circuitry). The videodecoder (510) can be used in place of the video decoder (410) in theexample of FIG. 4 .

The receiver (531) may receive one or more coded video sequences to bedecoded by the video decoder (510). In the same or another embodiment,one coded video sequence may be decoded at a time, where the decoding ofeach coded video sequence is independent from other coded videosequences. Each video sequence may be associated with multiple videoframes or images. The coded video sequence may be received from achannel (501), which may be a hardware/software link to a storage devicewhich stores the encoded video data or a streaming source whichtransmits the encoded video data. The receiver (531) may receive theencoded video data with other data such as coded audio data and/orancillary data streams, that may be forwarded to their respectiveprocessing circuitry (not depicted). The receiver (531) may separate thecoded video sequence from the other data. To combat network jitter, abuffer memory (515) may be disposed in between the receiver (531) and anentropy decoder/parser (520) (“parser (520)” henceforth). In certainapplications, the buffer memory (515) may be implemented as part of thevideo decoder (510). In other applications, it can be outside of andseparate from the video decoder (510) (not depicted). In still otherapplications, there can be a buffer memory (not depicted) outside of thevideo decoder (510) for the purpose of, for example, combating networkjitter, and there may be another additional buffer memory (515) insidethe video decoder (510), for example to handle playback timing. When thereceiver (531) is receiving data from a store/forward device ofsufficient bandwidth and controllability, or from an isosynchronousnetwork, the buffer memory (515) may not be needed, or can be small. Foruse on best-effort packet networks such as the Internet, the buffermemory (515) of sufficient size may be required, and its size can becomparatively large. Such buffer memory may be implemented with anadaptive size, and may at least partially be implemented in an operatingsystem or similar elements (not depicted) outside of the video decoder(510).

The video decoder (510) may include the parser (520) to reconstructsymbols (521) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (510),and potentially information to control a rendering device such asdisplay (512) (e.g., a display screen) that may or may not an integralpart of the electronic device (530) but can be coupled to the electronicdevice (530), as is shown in FIG. 5 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (520) mayparse/entropy-decode the coded video sequence that is received by theparser (520). The entropy coding of the coded video sequence can be inaccordance with a video coding technology or standard, and can followvarious principles, including variable length coding, Huffman coding,arithmetic coding with or without context sensitivity, and so forth. Theparser (520) may extract from the coded video sequence, a set ofsubgroup parameters for at least one of the subgroups of pixels in thevideo decoder, based upon at least one parameter corresponding to thesubgroups. The subgroups can include Groups of Pictures (GOPs),pictures, tiles, slices, macroblocks, Coding Units (CUs), blocks,Transform Units (TUs), Prediction Units (PUs) and so forth. The parser(520) may also extract from the coded video sequence information such astransform coefficients (e.g., Fourier transform coefficients), quantizerparameter values, motion vectors, and so forth.

The parser (520) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (515), so as tocreate symbols (521).

Reconstruction of the symbols (521) can involve multiple differentprocessing or functional units depending on the type of the coded videopicture or parts thereof (such as: inter and intra picture, inter andintra block), and other factors. The units that are involved and howthey are involved may be controlled by the subgroup control informationthat was parsed from the coded video sequence by the parser (520). Theflow of such subgroup control information between the parser (520) andthe multiple processing or functional units below is not depicted forsimplicity.

Beyond the functional blocks already mentioned, the video decoder (510)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these functional units interact closelywith each other and can, at least partly, be integrated with oneanother. However, for the purpose of describing the various functions ofthe disclosed subject matter with clarity, the conceptual subdivisioninto the functional units is adopted in the disclosure below.

A first unit may include the scaler/inverse transform unit (551). Thescaler/inverse transform unit (551) may receive a quantized transformcoefficient as well as control information, including informationindicating which type of inverse transform to use, block size,quantization factor/parameters, quantization scaling matrices, and thelie as symbol(s) (521) from the parser (520). The scaler/inversetransform unit (551) can output blocks comprising sample values that canbe input into aggregator (555).

In some cases, the output samples of the scaler/inverse transform (551)can pertain to an intra coded block, i.e., a block that does not usepredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (552). In some cases, the intra pictureprediction unit (552) may generate a block of the same size and shape ofthe block under reconstruction using surrounding block information thatis already reconstructed and stored in the current picture buffer (558).The current picture buffer (558) buffers, for example, partlyreconstructed current picture and/or fully reconstructed currentpicture. The aggregator (555), in some implementations, may add, on aper sample basis, the prediction information the intra prediction unit(552) has generated to the output sample information as provided by thescaler/inverse transform unit (551).

In other cases, the output samples of the scaler/inverse transform unit(551) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (553) canaccess reference picture memory (557) to fetch samples used forinter-picture prediction. After motion compensating the fetched samplesin accordance with the symbols (521) pertaining to the block, thesesamples can be added by the aggregator (555) to the output of thescaler/inverse transform unit (551) (output of unit 551 may be referredto as the residual samples or residual signal) so as to generate outputsample information. The addresses within the reference picture memory(557) from where the motion compensation prediction unit (553) fetchesprediction samples can be controlled by motion vectors, available to themotion compensation prediction unit (553) in the form of symbols (521)that can have, for example X, Y components (shift), and referencepicture components (time). Motion compensation may also includeinterpolation of sample values as fetched from the reference picturememory (557) when sub-sample exact motion vectors are in use, and mayalso be associated with motion vector prediction mechanisms, and soforth.

The output samples of the aggregator (555) can be subject to variousloop filtering techniques in the loop filter unit (556). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (556) as symbols (521) from the parser (520), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values. Several type of loop filters may beincluded as part of the loop filter unit 556 in various orders, as willbe described in further detail below.

The output of the loop filter unit (556) can be a sample stream that canbe output to the rendering device (512) as well as stored in thereference picture memory (557) for use in future inter-pictureprediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future inter-picture prediction. For example,once a coded picture corresponding to a current picture is fullyreconstructed and the coded picture has been identified as a referencepicture (by, for example, the parser (520)), the current picture buffer(558) can become a part of the reference picture memory (557), and afresh current picture buffer can be reallocated before commencing thereconstruction of the following coded picture.

The video decoder (510) may perform decoding operations according to apredetermined video compression technology adopted in a standard, suchas ITU-T Rec. H.265. The coded video sequence may conform to a syntaxspecified by the video compression technology or standard being used, inthe sense that the coded video sequence adheres to both the syntax ofthe video compression technology or standard and the profiles asdocumented in the video compression technology or standard.Specifically, a profile can select certain tools from all the toolsavailable in the video compression technology or standard as the onlytools available for use under that profile. To be standard-compliant,the complexity of the coded video sequence may be within bounds asdefined by the level of the video compression technology or standard. Insome cases, levels restrict the maximum picture size, maximum framerate, maximum reconstruction sample rate (measured in, for examplemegasamples per second), maximum reference picture size, and so on.Limits set by levels can, in some cases, be further restricted throughHypothetical Reference Decoder (HRD) specifications and metadata for HRDbuffer management signaled in the coded video sequence.

In some example embodiments, the receiver (531) may receive additional(redundant) data with the encoded video. The additional data may beincluded as part of the coded video sequence(s). The additional data maybe used by the video decoder (510) to properly decode the data and/or tomore accurately reconstruct the original video data. Additional data canbe in the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 6 shows a block diagram of a video encoder (603) according to anexample embodiment of the present disclosure. The video encoder (603)may be included in an electronic device (620). The electronic device(620) may further include a transmitter (640) (e.g., transmittingcircuitry). The video encoder (603) can be used in place of the videoencoder (403) in the example of FIG. 4 .

The video encoder (603) may receive video samples from a video source(601) (that is not part of the electronic device (620) in the example ofFIG. 6 ) that may capture video image(s) to be coded by the videoencoder (603). In another example, the video source (601) may beimplemented as a portion of the electronic device (620).

The video source (601) may provide the source video sequence to be codedby the video encoder (603) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 YCrCb, RGB, XYZ . . .), and any suitable sampling structure (for example YCrCb 4:2:0, YCrCb4:4:4). In a media serving system, the video source (601) may be astorage device capable of storing previously prepared video. In avideoconferencing system, the video source (601) may be a camera thatcaptures local image information as a video sequence. Video data may beprovided as a plurality of individual pictures or images that impartmotion when viewed in sequence. The pictures themselves may be organizedas a spatial array of pixels, wherein each pixel can comprise one ormore samples depending on the sampling structure, color space, and thelike being in use. A person having ordinary skill in the art can readilyunderstand the relationship between pixels and samples. The descriptionbelow focuses on samples.

According to some example embodiments, the video encoder (603) may codeand compress the pictures of the source video sequence into a codedvideo sequence (643) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speedconstitutes one function of a controller (650). In some embodiments, thecontroller (650) may be functionally coupled to and control otherfunctional units as described below. The coupling is not depicted forsimplicity. Parameters set by the controller (650) can include ratecontrol related parameters (picture skip, quantizer, lambda value ofrate-distortion optimization techniques, . . . ), picture size, group ofpictures (GOP) layout, maximum motion vector search range, and the like.The controller (650) can be configured to have other suitable functionsthat pertain to the video encoder (603) optimized for a certain systemdesign.

In some example embodiments, the video encoder (603) may be configuredto operate in a coding loop. As an oversimplified description, in anexample, the coding loop can include a source coder (630) (e.g.,responsible for creating symbols, such as a symbol stream, based on aninput picture to be coded, and a reference picture(s)), and a (local)decoder (633) embedded in the video encoder (603). The decoder (633)reconstructs the symbols to create the sample data in a similar manneras a (remote) decoder would create even though the embedded decoder 633process coded video steam by the source coder 630 without entropy coding(as any compression between symbols and coded video bitstream in entropycoding may be lossless in the video compression technologies consideredin the disclosed subject matter). The reconstructed sample stream(sample data) is input to the reference picture memory (634). As thedecoding of a symbol stream leads to bit-exact results independent ofdecoder location (local or remote), the content in the reference picturememory (634) is also bit exact between the local encoder and remoteencoder. In other words, the prediction part of an encoder “sees” asreference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used to improve coding quality.

The operation of the “local” decoder (633) can be the same as of a“remote” decoder, such as the video decoder (510), which has alreadybeen described in detail above in conjunction with FIG. 5 . Brieflyreferring also to FIG. 5 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (645) and the parser (520) can be lossless, the entropy decodingparts of the video decoder (510), including the buffer memory (515), andparser (520) may not be fully implemented in the local decoder (633) inthe encoder.

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that may only be presentin a decoder also may necessarily need to be present, in substantiallyidentical functional form, in a corresponding encoder. For this reason,the disclosed subject matter may at times focus on decoder operation,which allies to the decoding portion of the encoder. The description ofencoder technologies can thus be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas or aspects a more detail description of the encoder is providedbelow.

During operation in some example implementations, the source coder (630)may perform motion compensated predictive coding, which codes an inputpicture predictively with reference to one or more previously codedpicture from the video sequence that were designated as “referencepictures.” In this manner, the coding engine (632) codes differences (orresidue) in the color channels between pixel blocks of an input pictureand pixel blocks of reference picture(s) that may be selected asprediction reference(s) to the input picture. The term “residue” and itsadjective form “residual” may be used interchangeably.

The local video decoder (633) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (630). Operations of the coding engine (632) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 6 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (633) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (634). In this manner, the video encoder(603) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end (remote) video decoder (absent transmissionerrors).

The predictor (635) may perform prediction searches for the codingengine (632). That is, for a new picture to be coded, the predictor(635) may search the reference picture memory (634) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(635) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (635), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (634).

The controller (650) may manage coding operations of the source coder(630), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (645). The entropy coder (645)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compression of the symbols accordingto technologies such as Huffman coding, variable length coding,arithmetic coding, and so forth.

The transmitter (640) may buffer the coded video sequence(s) as createdby the entropy coder (645) to prepare for transmission via acommunication channel (660), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(640) may merge coded video data from the video coder (603) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (650) may manage operation of the video encoder (603).During coding, the controller (650) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person having ordinary skill in the art is aware of thosevariants of I pictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample coding blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16samples each) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures. The sourcepictures or the intermediate processed pictures may be subdivided intoother types of blocks for other purposes. The division of coding blocksand the other types of blocks may or may not follow the same manner, asdescribed in further detail below.

The video encoder (603) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (603) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data may accordingly conform to a syntax specified bythe video coding technology or standard being used.

In some example embodiments, the transmitter (640) may transmitadditional data with the encoded video. The source coder (630) mayinclude such data as part of the coded video sequence. The additionaldata may comprise temporal/spatial/SNR enhancement layers, other formsof redundant data such as redundant pictures and slices, SEI messages,VUI parameter set fragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) utilizes spatial correlation in a givenpicture, and inter-picture prediction utilizes temporal or othercorrelation between the pictures. For example, a specific picture underencoding/decoding, which is referred to as a current picture, may bepartitioned into blocks. A block in the current picture, when similar toa reference block in a previously coded and still buffered referencepicture in the video, may be coded by a vector that is referred to as amotion vector. The motion vector points to the reference block in thereference picture, and can have a third dimension identifying thereference picture, in case multiple reference pictures are in use.

In some example embodiments, a bi-prediction technique can be used forinter-picture prediction. According to such bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that both proceed the current picture in the video indecoding order (but may be in the past or future, respectively, indisplay order) are used. A block in the current picture can be coded bya first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bejointly predicted by a combination of the first reference block and thesecond reference block.

Further, a merge mode technique may be used in the inter-pictureprediction to improve coding efficiency.

According to some example embodiments of the disclosure, predictions,such as inter-picture predictions and intra-picture predictions areperformed in the unit of blocks. For example, a picture in a sequence ofvideo pictures is partitioned into coding tree units (CTU) forcompression, the CTUs in a picture may have the same size, such as 64×64pixels, 32×32 pixels, or 16×16 pixels. In general, a CTU may includethree parallel coding tree blocks (CTBs): one luma CTB and two chromaCTBs. Each CTU can be recursively quadtree split into one or multiplecoding units (CUs). For example, a CTU of 64×64 pixels can be split intoone CU of 64×64 pixels, or 4 CUs of 32×32 pixels. Each of the one ormore of the 32×32 block may be further split into 4 CUs of 16×16 pixels.In some example embodiments, each CU may be analyzed during encoding todetermine a prediction type for the CU among various prediction typessuch as an inter prediction type or an intra prediction type. The CU maybe split into one or more prediction units (PUs) depending on thetemporal and/or spatial predictability. Generally, each PU includes aluma prediction block (PB), and two chroma PBs. In an embodiment, aprediction operation in coding (encoding/decoding) is performed in theunit of a prediction block. The split of a CU into PU (or PBs ofdifferent color channels) may be performed in various spatial pattern. Aluma or chroma PB, for example, may include a matrix of values (e.g.,luma values) for samples, such as 8×8 pixels, 16×16 pixels, 8×16 pixels,16×8 samples, and the like.

FIG. 7 shows a diagram of a video encoder (703) according to anotherexample embodiment of the disclosure. The video encoder (703) isconfigured to receive a processing block (e.g., a prediction block) ofsample values within a current video picture in a sequence of videopictures, and encode the processing block into a coded picture that ispart of a coded video sequence. The example video encoder (703) may beused in place of the video encoder (403) in the FIG. 4 example.

For example, the video encoder (703) receives a matrix of sample valuesfor a processing block, such as a prediction block of 8×8 samples, andthe like. The video encoder (703) then determines whether the processingblock is best coded using intra mode, inter mode, or bi-prediction modeusing, for example, rate-distortion optimization (RDO). When theprocessing block is determined to be coded in intra mode, the videoencoder (703) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis determined to be coded in inter mode or bi-prediction mode, the videoencoder (703) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Insome example embodiments, a merge mode may be used as a submode of theinter picture prediction where the motion vector is derived from one ormore motion vector predictors without the benefit of a coded motionvector component outside the predictors. In some other exampleembodiments, a motion vector component applicable to the subject blockmay be present. Accordingly, the video encoder (703) may includecomponents not explicitly shown in FIG. 7 , such as a mode decisionmodule, to determine the perdition mode of the processing blocks.

In the example of FIG. 7 , the video encoder (703) includes an interencoder (730), an intra encoder (722), a residue calculator (723), aswitch (726), a residue encoder (724), a general controller (721), andan entropy encoder (725) coupled together as shown in the examplearrangement in FIG. 7 .

The inter encoder (730) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures in display order), generate inter predictioninformation (e.g., description of redundant information according tointer encoding technique, motion vectors, merge mode information), andcalculate inter prediction results (e.g., predicted block) based on theinter prediction information using any suitable technique. In someexamples, the reference pictures are decoded reference pictures that aredecoded based on the encoded video information using the decoding unit633 embedded in the example encoder 620 of FIG. 6 (shown as residualdecoder 728 of FIG. 7 , as described in further detail below).

The intra encoder (722) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to blocksalready coded in the same picture, and generate quantized coefficientsafter transform, and in some cases also to generate intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). The intra encoder (722) maycalculates intra prediction results (e.g., predicted block) based on theintra prediction information and reference blocks in the same picture.

The general controller (721) may be configured to determine generalcontrol data and control other components of the video encoder (703)based on the general control data. In an example, the general controller(721) determines the prediction mode of the block, and provides acontrol signal to the switch (726) based on the prediction mode. Forexample, when the prediction mode is the intra mode, the generalcontroller (721) controls the switch (726) to select the intra moderesult for use by the residue calculator (723), and controls the entropyencoder (725) to select the intra prediction information and include theintra prediction information in the bitstream; and when the predicationmode for the block is the inter mode, the general controller (721)controls the switch (726) to select the inter prediction result for useby the residue calculator (723), and controls the entropy encoder (725)to select the inter prediction information and include the interprediction information in the bitstream.

The residue calculator (723) may be configured to calculate a difference(residue data) between the received block and prediction results for theblock selected from the intra encoder (722) or the inter encoder (730).The residue encoder (724) may be configured to encode the residue datato generate transform coefficients. For example, the residue encoder(724) may be configured to convert the residue data from a spatialdomain to a frequency domain to generate the transform coefficients. Thetransform coefficients are then subject to quantization processing toobtain quantized transform coefficients. In various example embodiments,the video encoder (703) also includes a residual decoder (728). Theresidual decoder (728) is configured to perform inverse-transform, andgenerate the decoded residue data. The decoded residue data can besuitably used by the intra encoder (722) and the inter encoder (730).For example, the inter encoder (730) can generate decoded blocks basedon the decoded residue data and inter prediction information, and theintra encoder (722) can generate decoded blocks based on the decodedresidue data and the intra prediction information. The decoded blocksare suitably processed to generate decoded pictures and the decodedpictures can be buffered in a memory circuit (not shown) and used asreference pictures.

The entropy encoder (725) may be configured to format the bitstream toinclude the encoded block and perform entropy coding. The entropyencoder (725) is configured to include in the bitstream variousinformation. For example, the entropy encoder (725) may be configured toinclude the general control data, the selected prediction information(e.g., intra prediction information or inter prediction information),the residue information, and other suitable information in thebitstream. When coding a block in the merge submode of either inter modeor bi-prediction mode, there may be no residue information.

FIG. 8 shows a diagram of an example video decoder (810) according toanother embodiment of the disclosure. The video decoder (810) isconfigured to receive coded pictures that are part of a coded videosequence, and decode the coded pictures to generate reconstructedpictures. In an example, the video decoder (810) may be used in place ofthe video decoder (410) in the example of FIG. 4 .

In the example of FIG. 8 , the video decoder (810) includes an entropydecoder (871), an inter decoder (880), a residual decoder (873), areconstruction module (874), and an intra decoder (872) coupled togetheras shown in the example arrangement of FIG. 8 .

The entropy decoder (871) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (e.g., intra mode, intermode, bi-predicted mode, merge submode or another submode), predictioninformation (e.g., intra prediction information or inter predictioninformation) that can identify certain sample or metadata used forprediction by the intra decoder (872) or the inter decoder (880),residual information in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isthe inter or bi-predicted mode, the inter prediction information isprovided to the inter decoder (880); and when the prediction type is theintra prediction type, the intra prediction information is provided tothe intra decoder (872). The residual information can be subject toinverse quantization and is provided to the residual decoder (873).

The inter decoder (880) may be configured to receive the interprediction information, and generate inter prediction results based onthe inter prediction information.

The intra decoder (872) may be configured to receive the intraprediction information, and generate prediction results based on theintra prediction information.

The residual decoder (873) may be configured to perform inversequantization to extract de-quantized transform coefficients, and processthe de-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residual decoder (873) mayalso utilize certain control information (to include the QuantizerParameter (QP)) which may be provided by the entropy decoder (871) (datapath not depicted as this may be low data volume control informationonly).

The reconstruction module (874) may be configured to combine, in thespatial domain, the residual as output by the residual decoder (873) andthe prediction results (as output by the inter or intra predictionmodules as the case may be) to form a reconstructed block forming partof the reconstructed picture as part of the reconstructed video. It isnoted that other suitable operations, such as a deblocking operation andthe like, may also be performed to improve the visual quality.

It is noted that the video encoders (403), (603), and (703), and thevideo decoders (410), (510), and (810) can be implemented using anysuitable technique. In some example embodiments, the video encoders(403), (603), and (703), and the video decoders (410), (510), and (810)can be implemented using one or more integrated circuits. In anotherembodiment, the video encoders (403), (603), and (603), and the videodecoders (410), (510), and (810) can be implemented using one or moreprocessors that execute software instructions.

Turning to block partitioning for coding and decoding, generalpartitioning may start from a base block and may follow a predefinedruleset, particular patterns, partition trees, or any partitionstructure or scheme. The partitioning may be hierarchical and recursive.After dividing or partitioning a base block following any of the examplepartitioning procedures or other procedures described below, or thecombination thereof, a final set of partitions or coding blocks may beobtained. Each of these partitions may be at one of various partitioninglevels in the partitioning hierarchy, and may be of various shapes. Eachof the partitions may be referred to as a coding block (CB). For thevarious example partitioning implementations described further below,each resulting CB may be of any of the allowed sizes and partitioninglevels. Such partitions are referred to as coding blocks because theymay form units for which some basic coding/decoding decisions may bemade and coding/decoding parameters may be optimized, determined, andsignaled in an encoded video bitstream. The highest or deepest level inthe final partitions represents the depth of the coding blockpartitioning structure of tree. A coding block may be a luma codingblock or a chroma coding block. The CB tree structure of each color maybe referred to as coding block tree (CBT).

The coding blocks of all color channels may collectively be referred toas a coding unit (CU). The hierarchical structure of for all colorchannels may be collectively referred to as coding tree unit (CTU). Thepartitioning patterns or structures for the various color channels in ina CTU may or may not be the same.

In some implementations, partition tree schemes or structures used forthe luma and chroma channels may not need to be the same. In otherwords, luma and chroma channels may have separate coding tree structuresor patterns. Further, whether the luma and chroma channels use the sameor different coding partition tree structures and the actual codingpartition tree structures to be used may depend on whether the slicebeing coded is a P, B, or I slice. For example, For an I slice, thechroma channels and luma channel may have separate coding partition treestructures or coding partition tree structure modes, whereas for a P orB slice, the luma and chroma channels may share a same coding partitiontree scheme. When separate coding partition tree structures or modes areapplied, a luma channel may be partitioned into CBs by one codingpartition tree structure, and a chroma channel may be partitioned intochroma CBs by another coding partition tree structure.

In some example implementations, a predetermined partitioning patternmay be applied to a base block. As shown in FIG. 9 , an example 4-waypartition tree may start from a first predefined level (e.g., 64×64block level or other sizes, as a base block size) and a base block maybe partitioned hierarchically down to a predefined lowest level (e.g.,4×4 level). For example, a base block may be subject to four predefinedpartitioning options or patterns indicated by 902, 904, 906, and 908,with the partitions designated as R being allowed for recursivepartitioning in that the same partition options as indicated in FIG. 9may be repeated at a lower scale until the lowest level (e.g., 4×4level). In some implementations, additional restrictions may be appliedto the partitioning scheme of FIG. 9 . In the implementation of FIG. 9 ,rectangular partitions (e.g., 1:2/2:1 rectangular partitions) may beallowed but they may not be allowed to be recursive, whereas squarepartitions are allowed to be recursive. The partitioning following FIG.9 with recursion, if needed, generates a final set of coding blocks. Acoding tree depth may be further defined to indicate the splitting depthfrom the root node or root block. For example, the coding tree depth forthe root node or root block, e.g. a 64×64 block, may be set to 0, andafter the root block is further split once following FIG. 9 , the codingtree depth is increased by 1. The maximum or deepest level from 64×64base block to a minimum partition of 4×4 would be 4 (starting from level0) for the scheme above. Such partitioning scheme may apply to one ormore of the color channels. Each color channel may be partitionedindependently following the scheme of FIG. 9 (e.g., partitioning patternor option among the predefined patterns may be independently determinedfor each of the color channels at each hierarchical level).Alternatively, two or more of the color channels may share the samehierarchical pattern tree of FIG. 9 (e.g., the same partitioning patternor option among the predefined patterns may be chosen for the two ormore color channels at each hierarchical level).

FIG. 10 shows another example predefined partitioning pattern allowingrecursive partitioning to form a partitioning tree. As shown in FIG. 10, an example 10-way partitioning structure or pattern may be predefined.The root block may start at a predefined level (e.g. from a base blockat 128×128 level, or 64×64 level). The example partitioning structure ofFIG. 10 includes various 2:1/1:2 and 4:1/1:4 rectangular partitions. Thepartition types with 3 subpartitions indicated 1002, 1004, 1006, and1008 in the second row of FIG. 10 may be referred to “T-type”partitions. The “T-Type” partitions 1002, 1004, 1006, and 1008 may bereferred to as Left T-Type, Top T-Type, Right T-Type and Bottom T-Type.In some example implementations, none of the rectangular partitions ofFIG. 10 is allowed to be further subdivided. A coding tree depth may befurther defined to indicate the splitting depth from the root node orroot block. For example, the coding tree depth for the root node or rootblock, e.g., a 128×128 block, may be set to 0, and after the root blockis further split once following FIG. 10 , the coding tree depth isincreased by 1. In some implementations, only the all-square partitionsin 1010 may be allowed for recursive partitioning into the next level ofthe partitioning tree following pattern of FIG. 10 . In other words,recursive partitioning may not be allowed for the square partitionswithin the T-type patterns 1002, 1004, 1006, and 1008. The partitioningprocedure following FIG. 10 with recursion, if needed, generates a finalset of coding blocks. Such scheme may apply to one or more of the colorchannels. In some implementations, more flexibility may be added to theuse of partitions below 8×8 level. For example, 2×2 chroma interprediction may be used in certain cases.

In some other example implementations for coding block partitioning, aquadtree structure may be used for splitting a base block or anintermediate block into quadtree partitions. Such quadtree splitting maybe applied hierarchically and recursively to any square shapedpartitions. Whether a base block or an intermediate block or partitionis further quadtree split may be adapted to various localcharacteristics of the base block or intermediate block/partition.Quadtree partitioning at picture boundaries may be further adapted. Forexample, implicit quadtree split may be performed at picture boundary sothat a block will keep quadtree splitting until the size fits thepicture boundary.

In some other example implementations, a hierarchical binarypartitioning from a base block may be used. For such a scheme, the baseblock or an intermediate level block may be partitioned into twopartitions. A binary partitioning may be either horizontal or vertical.For example, a horizontal binary partitioning may split a base block orintermediate block into equal right and left partitions. Likewise, avertical binary partitioning may split a base block or intermediateblock into equal upper and lower partitions. Such binary partitioningmay be hierarchical and recursive. Decision may be made at each of thebase block or intermediate block whether the binary partitioning schemeshould continue, and if the scheme does continue further, whether ahorizontal or vertical binary partitioning should be used. In someimplementations, further partitioning may stop at a predefined lowestpartition size (in either one or both dimensions). Alternatively,further partitioning may stop once a predefined partitioning level ordepth from the base block is reached. In some implementations, theaspect ratio of a partition may be restricted. For example, the aspectratio of a partition may not be smaller than 1:4 (or larger than 4:1).As such, a vertical strip partition with vertical to horizontal aspectratio of 4:1, may only be further binary partitioned vertically into anupper and lower partitions each having a vertical to horizontal aspectratio of 2:1.

In yet some other examples, a ternary partitioning scheme may be usedfor partitioning a base block or any intermediate block, as shown inFIG. 13 . The ternary pattern may be implemented vertical, as shown in1302 of FIG. 13 , or horizontal, as shown in 1304 of FIG. 13 . While theexample split ratio in FIG. 13 , either vertically or horizontally, isshown as 1:2:1, other ratios may be predefined. In some implementations,two or more different ratios may be predefined. Such ternarypartitioning scheme may be used to complement the quadtree or binarypartitioning structures in that such triple-tree partitioning is capableof capturing objects located in block center in one contiguous partitionwhile quadtree and binary-tree are always splitting along block centerand thus would split the object into separate partitions. In someimplementations, the width and height of the partitions of the exampletriple trees are always power of 2 to avoid additional transforms.

The above partitioning schemes may be combined in any manner atdifferent partitioning levels. As one example, the quadtree and thebinary partitioning schemes described above may be combined to partitiona base block into a quadtree-binary-tree (QTBT) structure. In such ascheme, a base block or an intermediate block/partition may be eitherquadtree split or binary split, subject to a set of predefinedconditions, if specified. A particular example is illustrated in FIG. 14. In the example of FIG. 14 , a base block is first quadtree split intofour partitions, as shown by 1402, 1404, 1406, and 1408. Thereafter,each of the resulting partitions is either quadtree partitioned intofour further partitions (such as 1408), or binarily split into twofurther partitions (either horizontally or vertically, such as 1402 or1406, both being symmetric, for example) at the next level, or non-split(such as 1404). Binary or quadtree splitting may be allowed recursivelyfor square shaped partitions, as shown by the overall example partitionpattern of 1410 and the corresponding tree structure/representation in1420, in which the solid lines represent quadtree splitting, and thedashed lines represent binary splitting. Flags may be used for eachbinary splitting node (non-leaf binary partitions) to indicate whetherthe binary splitting is horizontal or vertical. For example, as shown in1420, consistent with the partitioning structure of 1410, flag “0” mayrepresent horizontal binary splitting, and flag “1” may representvertical binary splitting. For the quadtree-split partition, there is noneed to indicate the splitting type since quadtree splitting alwayssplits a block or a partition both horizontally and vertically toproduce 4 sub-blocks/partitions with an equal size. In someimplementations, flag “1” may represent horizontal binary splitting, andflag “0” may represent vertical binary splitting.

In some example implementations of the QTBT, the quadtree and binarysplitting ruleset may be represented by the following predefinedparameters and the corresponding functions associated therewith:

CTU size: the root node size of a quadtree (size of a base block)

MinQTSize: the minimum allowed quadtree leaf node size

MaxBTSize: the maximum allowed binary tree root node size

MaxBTDepth: the maximum allowed binary tree depth

MinBTSize: the minimum allowed binary tree leaf node size

In some example implementations of the QTBT partitioning structure, theCTU size may be set as 128×128 luma samples with two corresponding 64×64blocks of chroma samples (when an example chroma sub-sampling isconsidered and used), the MinQTSize may be set as 16×16, the MaxBTSizemay be set as 64×64, the MinBTSize (for both width and height) may beset as 4×4, and the MaxBTDepth may be set as 4. The quadtreepartitioning may be applied to the CTU first to generate quadtree leafnodes. The quadtree leaf nodes may have a size from its minimum allowedsize of 16×16 (i.e., the MinQTSize) to 128×128 (i.e., the CTU size). Ifa node is 128×128, it will not be first split by the binary tree sincethe size exceeds the MaxBTSize (i.e., 64×64). Otherwise, nodes which donot exceed MaxBTSize could be partitioned by the binary tree. In theexample of FIG. 14 , the base block is 128×128. The basic block can onlybe quadtree split, according to the predefined ruleset. The base blockhas a partitioning depth of 0. Each of the resulting four partitions are64×64, not exceeding MaxBTSize, may be further quadtree or binary-treesplit at level 1. The process continues. When the binary tree depthreaches MaxBTDepth (i.e., 4), no further splitting may be considered.When the binary tree node has width equal to MinBTSize (i.e., 4), nofurther horizontal splitting may be considered. Similarly, when thebinary tree node has height equal to MinBTSize, no further verticalsplitting is considered.

In some example implementations, the QTBT scheme above may be configuredto support a flexibility for the luma and chroma to have the same QTBTstructure or separate QTBT structures. For example, for P and B slices,the luma and chroma CTBs in one CTU may share the same QTBT structure.However, for I slices, the luma CTBs maybe partitioned into CBs by aQTBT structure, and the chroma CTBs may be partitioned into chroma CBsby another QTBT structure. This means that a CU may be used to refer todifferent color channels in an I slice, e.g., the I slice may consist ofa coding block of the luma component or coding blocks of two chromacomponents, and a CU in a P or B slice may consist of coding blocks ofall three colour components.

In some other implementations, the QTBT scheme may be supplemented withternary scheme described above. Such implementations may be referred toas multi-type-tree (MTT) structure. For example, in addition to binarysplitting of a node, one of the ternary partition patterns of FIG. 13may be chosen. In some implementations, only square nodes may be subjectto ternary splitting. An additional flag may be used to indicate whethera ternary partitioning is horizontal or vertical.

The design of two-level or multi-level tree such as the QTBTimplementations and QTBT implementations supplemented by ternarysplitting may be mainly motivated by complexity reduction.Theoretically, the complexity of traversing a tree is T^(D), where Tdenotes the number of split types, and D is the depth of tree. Atradeoff may be made by using multiple types (T) while reducing thedepth (D).

In some implementations, a CB may be further partitioned. For example, aCB may be further partitioned into multiple prediction blocks (PBs) forpurposes of intra or inter-frame prediction during coding and decodingprocesses. In other words, a CB may be further divided into differentsubpartitions, where individual prediction decision/configuration may bemade. In parallel, a CB may be further partitioned into a plurality oftransform blocks (TBs) for purposes of delineating levels at whichtransform or inverse transform of video data is performed. Thepartitioning scheme of a CB into PBs and TBs may or may not be the same.For example, each partitioning scheme may be performed using its ownprocedure based on, for example, the various characteristics of thevideo data. The PB and TB partitioning schemes may be independent insome example implementations. The PB and TB partitioning schemes andboundaries may be correlated in some other example implementations. Isome implementations, for example, TBs may be partitioned after PBpartitions, and in particular, each PB, after being determined followingpartitioning of a coding block, may then be further partitioned into oneor more TBs. For example, in some implementations, a PB may be splitinto one, two, four, or other number of TBs.

In some implementations, for partitioning of a base block into codingblocks and further into prediction blocks and/or transform blocks, theluma channel and the chroma channels may be treated differently. Forexample, in some implementations, partitioning of a coding block intoprediction blocks and/or transform blocks may be allowed for the lumachannel, whereas such partitioning of a coding block into predictionblocks and/or transform blocks may not be allowed for the chromachannel(s). In such implementations, transform and/or prediction of lumablocks thus may be performed only at the coding block level. For anotherexample, minimum transform block size for luma channel and chromachannel(s) may be different, e.g., coding blocks for luma channel may beallowed to be partitioned into smaller transform and/or predictionblocks than the chroma channels. For yet another example, the maximumdepth of partitioning of a coding block into transform blocks and/orprediction blocks may be different between the luma channel and thechroma channels, e.g., coding blocks for luma channel may be allowed tobe partitioned into deeper transform and/or prediction blocks than thechroma channel(s). For a specific example, luma coding blocks may bepartitioned into transform blocks of multiple sizes that can berepresented by a recursive partition going down by up to 2 levels, andtransform block shapes such as square, 2:1/1:2, and 4:1/1:4 andtransform block size from 4×4 to 64×64 may be allowed. For chromablocks, however, only the largest possible transform blocks specifiedfor the luma blocks may be allowed.

In some example implementations for partitioning of a coding block intoPBs, the depth, the shape, and/or other characteristics of the PBpartitioning may depend on whether the PB is intra or inter coded.

The partitioning of a coding block (or a prediction block) intotransform blocks may be implemented in various example schemes,including but not limited to quadtree splitting and predefined patternsplitting, recursively or non-recursively, and with additionalconsideration for transform blocks at the boundary of the coding blockor prediction block. In general, the resulting transform blocks may beat different split levels, may not be of the same size, and may not needto be square in shape (e.g., they can be rectangular with some allowedsizes and aspect ratios). Further examples are descried in furtherdetail below in relation to FIGS. 15, 16 and 17 .

In some other implementations, however, the CBs obtained via any of thepartitioning schemes above may be used as a basic or smallest codingblock for prediction and/or transform. In other words, no furthersplitting is performed for perform inter-prediction/intra-predictionpurposes and/or for transform purposes. For example, CBs obtained fromthe QTBT scheme above may be directly used as the units for performingpredictions. Specifically, such a QTBT structure removes the concepts ofmultiple partition types, i.e. it removes the separation of the CU, PUand TU, and supports more flexibility for CU/CB partition shapes asdescribed above. In such QTBT block structure, a CU/CB can have either asquare or rectangular shape. The leaf nodes of such QTBT are used asunits for prediction and transform processing without any furtherpartitioning. This means that the CU, PU and TU have the same block sizein such example QTBT coding block structure.

The various CB partitioning schemes above and the further partitioningof CBs into PBs and/or TBs (including no PB/TB partitioning) may becombined in any manner. The following particular implementations areprovided as non-limiting examples.

A specific example implementation of coding block and transform blockpartitioning is described below. In such an example implementation, abase block may be split into coding blocks using recursive quadtreesplitting, or a predefined splitting pattern described above (such asthose in FIG. 9 and FIG. 10 ). At each level, whether further quadtreesplitting of a particular partition should continue may be determined bylocal video data characteristics. The resulting CBs may be at variousquadtree splitting levels, and of various sizes. The decision on whetherto code a picture area using inter-picture (temporal) or intra-picture(spatial) prediction may be made at the CB level (or CU level, for allthree-color channels). Each CB may be further split into one, two, four,or other number of PBs according to predefined PB splitting type. Insideone PB, the same prediction process may be applied and the relevantinformation may be transmitted to the decoder on a PB basis. Afterobtaining the residual block by applying the prediction process based onthe PB splitting type, a CB can be partitioned into TBs according toanother quadtree structure similar to the coding tree for the CB. Inthis particular implementation, a CB or a TB may but does not have to belimited to square shape. Further in this particular example, a PB may besquare or rectangular shape for an inter-prediction and may only besquare for intra-prediction. A coding block may be split into, e.g.,four square-shaped TBs. Each TB may be further split recursively (usingquadtree split) into smaller TBs, referred to as Residual Quadtree(RQT).

Another example implementation for partitioning of a base block intoCBs, PBs and or TBs is further described below. For example, rather thanusing a multiple partition unit types such as those shown in FIG. 9 orFIG. 10 , a quadtree with nested multi-type tree using binary andternary splits segmentation structure (e.g., the QTBT or QTBT withternary splitting as descried above) may be used. The separation of theCB, PB and TB (i.e., the partitioning of CB into PBs and/or TBs, and thepartitioning of PBs into TBs) may be abandoned except when needed forCBs that have a size too large for the maximum transform length, wheresuch CBs may need further splitting. This example partitioning schememay be designed to support more flexibility for CB partition shapes sothat the prediction and transform can both be performed on the CB levelwithout further partitioning. In such a coding tree structure, a CB mayhave either a square or rectangular shape. Specifically, a coding treeblock (CTB) may be first partitioned by a quadtree structure. Then thequadtree leaf nodes may be further partitioned by a nested multi-typetree structure. An example of the nested multi-type tree structure usingbinary or ternary splitting is shown in FIG. 11 . Specifically, theexample multi-type tree structure of FIG. 11 includes four splittingtypes, referred to as vertical binary splitting (SPLIT_BT_VER) (1102),horizontal binary splitting (SPLIT_BT_HOR) (1104), vertical ternarysplitting (SPLIT_TT_VER) (1106), and horizontal ternary splitting(SPLIT_TT_HOR) (1108). The CBs then correspond to leaves of themulti-type tree. In this example implementation, unless the CB is toolarge for the maximum transform length, this segmentation is used forboth prediction and transform processing without any furtherpartitioning. This means that, in most cases, the CB, PB and TB have thesame block size in the quadtree with nested multi-type tree coding blockstructure. The exception occurs when maximum supported transform lengthis smaller than the width or height of the colour component of the CB.In some implementations, in addition to the binary or ternary splitting,the nested patterns of FIG. 11 may further include quadtree splitting.

One specific example for the quadtree with nested multi-type tree codingblock structure of block partition (including quadtree, binary, andternary splitting options) for one base block is shown in FIG. 12 . Inmore detail, FIG. 12 shows that the base block 1200 is quadtree splitinto four square partitions 1202, 1204, 1206, and 1208. Decision tofurther use the multi-type tree structure of FIG. 11 and quadtree forfurther splitting is made for each of the quadtree-split partitions. Inthe example of FIG. 12 , partition 1204 is not further split. Partitions1202 and 1208 each adopt another quadtree split. For partition 1202, thesecond level quadtree-split top-left, top-right, bottom-left, andbottom-right partitions adopts third level splitting of quadtree,horizontal binary splitting 1104 of FIG. 11 , non-splitting, andhorizontal ternary splitting 1108 of FIG. 11 , respectively. Partition1208 adopts another quadtree split, and the second level quadtree-splittop-left, top-right, bottom-left, and bottom-right partitions adoptsthird level splitting of vertical ternary splitting 1106 of FIG. 11 ,non-splitting, non-splitting, and horizontal binary splitting 1104 ofFIG. 11 , respectively. Two of the subpartitions of the third-leveltop-left partition of 1208 are further split according to horizontalbinary splitting 1104 and horizontal ternary splitting 1108 of FIG. 11 ,respectively. Partition 1206 adopts a second level split patternfollowing the vertical binary splitting 1102 of FIG. 11 into twopartitions which are further split in a third-level according tohorizontal ternary splitting 1108 and vertical binary splitting 1102 ofthe FIG. 11 . A fourth level splitting is further applied to one of themaccording to horizontal binary splitting 1104 of FIG. 11 .

For the specific example above, the maximum luma transform size may be64×64 and the maximum supported chroma transform size could be differentfrom the luma at, e.g., 32×32. Even though the example CBs above in FIG.12 are generally not further split into smaller PBs and/or TBs, when thewidth or height of the luma coding block or chroma coding block islarger than the maximum transform width or height, the luma coding blockor chroma coding block may be automatically split in the horizontaland/or vertical direction to meet the transform size restriction in thatdirection.

In the specific example for partitioning of a base block into CBs above,and as descried above, the coding tree scheme may support the abilityfor the luma and chroma to have a separate block tree structure. Forexample, for P and B slices, the luma and chroma CTBs in one CTU mayshare the same coding tree structure. For I slices, for example, theluma and chroma may have separate coding block tree structures. Whenseparate block tree structures are applied, luma CTB may be partitionedinto luma CBs by one coding tree structure, and the chroma CTBs arepartitioned into chroma CBs by another coding tree structure. This meansthat a CU in an I slice may consist of a coding block of the lumacomponent or coding blocks of two chroma components, and a CU in a P orB slice always consists of coding blocks of all three colour componentsunless the video is monochrome.

When a coding block is further partitioned into multiple transformblocks, the transform blocks therein may be order in the bitstreamfollowing various order or scanning manners. Example implementations forpartitioning a coding block or prediction block into transform blocks,and a coding order of the transform blocks are described in furtherdetail below. In some example implementations, as descried above, atransform partitioning may support transform blocks of multiple shapes,e.g., 1:1 (square), 1:2/2:1, and 1:4/4:1, with transform block sizesranging from, e.g., 4×4 to 64×64. In some implementations, if the codingblock is smaller than or equal to 64×64, the transform blockpartitioning may only apply to luma component, such that for chromablocks, the transform block size is identical to the coding block size.Otherwise, if the coding block width or height is greater than 64, thenboth the luma and chroma coding blocks may be implicitly split intomultiples of min (W, 64)×min (H, 64) and min (W, 32)×min (H, 32)transform blocks, respectively.

In some example implementations of transform block partitioning, forboth intra and inter coded blocks, a coding block may be furtherpartitioned into multiple transform blocks with a partitioning depth upto a predefined number of levels (e.g., 2 levels). The transform blockpartitioning depth and sizes may be related. For some exampleimplementations, a mapping from the transform size of the current depthto the transform size of the next depth is shown in the following inTable 1.

TABLE 1 Transform partition size setting Transform Size of TransformSize of Current Depth Next Depth TX_4 × 4 TX_4 × 4 TX_8 × 8 TX_4 × 4TX_16 × 16 TX_8 × 8 TX_32 × 32 TX_16 × 16 TX_64 × 64 TX_32 × 32 TX_4 × 8TX_4 × 4 TX_8 × 4 TX_4 × 4 TX_8 × 16 TX_8 × 8 TX_16 × 8 TX_8 × 8 TX_16 ×32 TX_16 × 16 TX_32 × 16 TX_16 × 16 TX_32 × 64 TX_32 × 32 TX_64 × 32TX_32 × 32 TX_4 × 16 TX_4 × 8 TX_16 × 4 TX_8 × 4 TX_8 × 32 TX_8 × 16TX_32 × 8 TX_16 × 8 TX_16 × 64 TX_16 × 32 TX_64 × 16 TX_32 × 16

Based on the example mapping of Table 1, for 1:1 square block, the nextlevel transform split may create four 1:1 square sub-transform blocks.Transform partition may stop, for example, at 4×4. As such, a transformsize for a current depth of 4×4 corresponds to the same size of 4×4 forthe next depth. In the example of Table 1, for 1:2/2:1 non-square block,the next level transform split may create two 1:1 square sub-transformblocks, whereas for 1:4/4:1 non-square block, the next level transformsplit may create two 1:2/2:1 sub transform blocks.

In some example implementations, for luma component of an intra codedblock, additional restriction may be applied with respect to transformblock partitioning. For example, for each level of transformpartitioning, all the sub-transform blocks may be restricted to havingequal size. For example, for a 32×16 coding block, level 1 transformsplit creates two 16×16 sub-transform blocks, level 2 transform splitcreates eight 8×8 sub-transform blocks. In other words, the second levelsplitting must be applied to all first level sub blocks to keep thetransform units at equal sizes. An example of the transform blockpartitioning for intra coded square block following Table 1 is shown inFIG. 15 , together with coding order illustrated by the arrows.Specifically, 1502 shows the square coding block. A first-level splitinto 4 equal sized transform blocks according to Table 1 is shown in1504 with coding order indicated by the arrows. A second-level split ofall of the first-level equal sized blocks into 16 equal sized transformblocks according to Table 1 is shown in 1506 with coding order indicatedby the arrows.

In some example implementations, for luma component of inter codedblock, the above restriction for intra coding may not be applied. Forexample, after the first level of transform splitting, any one ofsub-transform block may be further split independently with one morelevel. The resulting transform blocks thus may or may not be of the samesize. An example split of an inter coded block into transform locks withtheir coding order is show in FIG. 16 . In the Example of FIG. 16 , theinter coded block 1602 is split into transform blocks at two levelsaccording to Table 1. At the first level, the inter coded block is splitinto four transform blocks of equal size. Then only one of the fourtransform blocks (not all of them) is further split into foursub-transform blocks, resulting in a total of 7 transform blocks havingtwo different sizes, as shown by 1604. The example coding order of these7 transform blocks is shown by the arrows in 1604 of FIG. 16 .

In some example implementations, for chroma component(s), someadditional restriction for transform blocks may apply. For example, forchroma component(s) the transform block size can be as large as thecoding block size, but not smaller than a predefined size, e.g., 8×8.

In some other example implementations, for the coding block with eitherwidth (W) or height (H) being greater than 64, both the luma and chromacoding blocks may be implicitly split into multiples of min (W, 64)×min(H, 64) and min (W, 32)×min (H, 32) transform units, respectively. Here,in the present disclosure, a “min (a, b)” may return a smaller valuebetween a and b.

FIG. 17 further shows another alternative example scheme forpartitioning a coding block or prediction block into transform blocks.As shown in FIG. 17 , instead of using recursive transform partitioning,a predefined set of partitioning types may be applied to a coding blockaccording a transform type of the coding block. In the particularexample shown in FIG. 17 , one of the 6 example partitioning types maybe applied to split a coding block into various number of transformblocks. Such scheme of generating transform block partitioning may beapplied to either a coding block or a prediction block.

In more detail, the partitioning scheme of FIG. 17 provides up to 6example partition types for any given transform type (transform typerefers to the type of, e.g., primary transform, such as ADST andothers). In this scheme, every coding block or prediction block may beassigned a transform partition type based on, for example, arate-distortion cost. In an example, the transform partition typeassigned to the coding block or prediction block may be determined basedon the transform type of the coding block or prediction block. Aparticular transform partition type may correspond to a transform blocksplit size and pattern, as shown by the 6 transform partition typesillustrated in FIG. 17 . A correspondence relationship between varioustransform types and the various transform partition types may bepredefined. An example is shown below with the capitalized labelsindicating the transform partition types that may be assigned to thecoding block or prediction block based on rate distortion cost:

-   -   PARTITION_NONE: Assigns a transform size that is equal to the        block size.    -   PARTITION_SPLIT: Assigns a transform size that is ½ the width of        the block size and ½ the height of the block size.    -   PARTITION_HORZ: Assigns a transform size with the same width as        the block size and ½ the height of the block size.    -   PARTITION_VERT: Assigns a transform size with ½ the width of the        block size and the same height as the block size.    -   PARTITION_HORZ4: Assigns a transform size with the same width as        the block size and ¼ the height of the block size.    -   PARTITION_VERT4: Assigns a transform size with ¼ the width of        the block size and the same height as the block size.

In the example above, the transform partition types as shown in FIG. 17all contain uniform transform sizes for the partitioned transformblocks. This is a mere example rather than a limitation. In some otherimplementations, mixed transform blocks sizes may be used for thepartitioned transform blocks in a particular partition type (orpattern).

The PBs (or CBs, also referred to as PBs when not being furtherpartitioned into prediction blocks) obtained from any of thepartitioning schemes above may then become the individual blocks forcoding via either intra or inter predictions. For inter-prediction for acurrent PB, a residual between the current block and a prediction blockmay be generated, coded, and included in the coded bitstream.

Inter-prediction may be implemented, for example, in a single-referencemode or a compound-reference mode. In some implementations, a skip flagmay be first included in the bitstream for a current block (or at ahigher level) to indicate whether the current block is inter-coded andis not to be skipped. If the current block is inter-coded, then anotherflag may be further included in the bitstream as a signal to indicatewhether the single-reference mode or compound-reference mode is used forthe prediction of the current block. For the single-reference mode, onereference block may be used to generate the prediction block for thecurrent block. For the compound-reference mode, two or more referenceblocks may be used to generate the prediction block by, for example,weighted average. The compound-reference mode may be referred asmore-than-one-reference mode, two-reference mode, or multiple-referencemode. The reference block or reference blocks may be identified usingreference frame index or indices and additionally using correspondingmotion vector or motion vectors which indicate shift(s) between thereference block(s) and the current blocks in location, e.g., inhorizontal and vertical pixels. For example, the inter-prediction blockfor the current block may be generated from a single-reference blockidentified by one motion vector in a reference frame as the predictionblock in the single-reference mode, whereas for the compound-referencemode, the prediction block may be generated by a weighted average of tworeference blocks in two reference frames indicated by two referenceframe indices and two corresponding motion vectors. The motion vector(s)may be coded and included in the bitstream in various manners.

In some implementations, an encoding or decoding system may maintain adecoded picture buffer (DPB). Some images/pictures may be maintained inthe DPB waiting for being displayed (in a decoding system) and someimages/pictures in the DPB may be used as reference frames to enableinter-prediction (in a decoding system or encoding system). In someimplementations, the reference frames in the DPB may be tagged as eithershort-term references or long-term references for a current image beingencoded or decoded. For example, short-term reference frames may includeframes that are used for inter-prediction for blocks in a current frameor in a predefined number (e.g., 2) of closest subsequent video framesto the current frame in a decoding order. The long-term reference framesmay include frames in the DPB that can be used to predict image blocksin frames that are more than the predefined number of frames away fromthe current frame in the order of decoding. Information about such tagsfor short and long-term reference frames may be referred to as ReferencePicture Set (RPS) and may be added to a header of each frame in theencoded bitstream. Each frame in the encoded video stream may beidentified by a Picture Order Counter (POC), which is numbered accordingto playback sequence in an absolute manner or relevant to a picturegroup starting from, for example, an I-frame.

In some example implementations, one or more reference picture listscontaining identification of short-term and long-term reference framesfor inter-prediction may be formed based on the information in the RPS.For example, a single picture reference list may be formed foruni-directional inter-prediction, denoted as L0 reference (or referencelist 0) whereas two picture referenced lists may be formed forbi-direction inter-prediction, denoted as L0 (or reference list 0) andL1 (or reference list 1) for each of the two prediction directions. Thereference frames included in the L0 and L1 lists may be ordered invarious predetermined manners. The lengths of the L0 and L1 lists may besignaled in the video bitstream. Uni-directional inter-prediction may beeither in the single-reference mode, or in the compound-reference modewhen the multiple references for the generation of prediction block byweighted average in the compound prediction mode are on a same side ofthe block to be predicted. Bi-directional inter-prediction may only becompound mode in that bi-directional inter-prediction involves at leasttwo reference blocks.

Adaptive Loop Filter

In Versatile Video Coding (VVC), an Adaptive Loop Filter (ALF) withblock-based filter adaption is applied. For the luma component, oneamong many filters is selected for each 4×4 block, based on thedirection and activity of local gradients. In one example, there may be25 filters to select from.

FIG. 18 shows an example adaptive loop filter (ALF) shape. Specifically,FIG. 18 illustrates two diamond filter shapes. The 7×7 diamond shape isapplied for luma component and the 5×5 diamond shape is applied forchroma components.

The block classification can be calculated for different examples asfollows. For luma component, each 4×4 block is categorized into one outof 25 classes. The classification index C is derived based on itsdirectionality D and a quantized value of activity Â, as follows:

C=5D+Â  (1)

To calculate D and Â, gradients of the horizontal, vertical and twodiagonal direction are first calculated using 1-D Laplacian:

g _(v)=Σ_(k=i−2) ^(i+3)Σ_(l=j−2) ^(j+3) V _(k,l) , V_(k,l)=|2R(k,l)−R(k,l−1)−R(k,l+1)|  (2)

g _(h)=Σ_(k=i−2) ^(i+3)Σ_(l=j−2) ^(j+3) H _(k,l) , H_(k,l)=|2R(k,l)−R(k−1,l)−R(k+1l)|  (3)

g _(d1)=Σ_(k=i−2) ^(i+3)Σ_(l=j−3) ^(j+3) D1_(k,l) ,D1_(k,l)=|2R(k,l)−R(k−1,l−1)−R(k+1,l+1)|  (4)

g _(d2)=Σ_(k=i−2) ^(i+3)Σ_(j=j−2) ^(j+3) D2_(k,l) ,D2_(k,l)=|2R(k,l)−R(k−1,l+1)−R(k+1,l−1)|  (5)

Where indices i and j refer to the coordinates of the upper left samplewithin the 4×4 block and R(i, j) indicates a reconstructed sample atcoordinate (i, j).

To reduce the complexity of block classification, the subsampled 1-DLaplacian calculation may be applied. As shown in FIGS. 19 a-19 d , thesame subsampled positions may be used for gradient calculation of alldirections. FIG. 19 a shows subsampled positions in a Laplaciancalculation for a vertical gradient. FIG. 19 b shows subsampledpositions in a Laplacian calculation for a horizontal gradient. FIG. 19c shows subsampled positions in a Laplacian calculation for a diagonalgradient. FIG. 19 d shows subsampled positions in a Laplaciancalculation for another diagonal gradient.

Then D maximum and minimum values of the gradients of horizontal andvertical directions are set as:

g _(h,v) ^(max)=max(g _(h) ,g _(v)), g _(h,v) ^(min)=min(g _(h) ,g_(v))  (6)

The maximum and minimum values of the gradient of two diagonaldirections are set as:

g _(d1,d2) ^(max)=max(g _(d1) ,g _(d2)), g _(d1,d2) ^(min)=min(g _(d1),g _(d2))  (7)

To derive the value of the directionality D, these values are comparedagainst each other and with two thresholds t₁ and t₂:Step 1. If both g_(h,v) ^(max)≤t₁·g_(h,v) ^(min) and g_(d1,d2)^(max)≤t₁·g_(d1,d2) ^(min) are true, D is set to 0.Step 2. If g_(h,v) ^(max)/g_(h,v) ^(min)>g_(d1,d2) ^(max)/g_(d1,d2)^(min), continue from Step 3; otherwise continue from Step 4.Step 3. If g_(h,v) ^(max)>t₂·g_(h,v) ^(min), D is set to 2; otherwise Dis set to 1.Step 4. If g_(d1,d2) ^(max)>t₂·g_(d1,d2) ^(min), D is set to 4;otherwise D is set to 3.The activity value A is calculated as:

A=Σ _(k=i−2) ^(i+3)Σ_(l=j−2) ^(j+3)(V _(k,l) +H _(k,l))  (8)

A is further quantized to the range of 0 to 4, inclusively, and thequantized value is denoted as Â. For chroma components in a picture, noclassification method is applied. In other words, a single set of ALFcoefficients may be applied for each chroma component.

There may be a geometric transformation of filter coefficients andclipping values. Before filtering each 4×4 luma block, geometrictransformations such as rotation or diagonal and vertical flipping maybe applied to the filter coefficients f(k, l) and to the correspondingfilter clipping values c(k, l) depending on gradient values calculatedfor that block. This may be equivalent to applying these transformationsto the samples in the filter support region. This can make differentblocks to which ALF is applied more uniformly by aligning theirdirectionality. Three geometric transformations may include diagonal,vertical flip and rotation:

Diagonal: f _(D)(k,l)=f(l,k), c _(D)(k,l)=c(l,k),  (9)

Vertical flip: f _(V)(k,l)=f(k,K−l−1), c _(V)(k,l)=c(k,K−l−1)  (10)

Rotation: f _(R)(k,l)=f(K−l−1,k), c _(R)(k,l)=c(K−l−1,k)  (11)

where K is the size of the filter and 0≤k, l≤K−1 are coefficientscoordinates, such that location (0,0) is at the upper left corner andlocation (K−1, K−1) is at the lower right corner. The transformationsare applied to the filter coefficients f (k, l) and to the clippingvalues c(k, l) depending on gradient values calculated for that block.The relationship between the transformation and the four gradients ofthe four directions are summarized in the following Table 2:

TABLE 2 Mapping of the gradient calculated for one block and thetransformations Gradient values Transformation g_(d2) < g_(d1) and g_(h)< g_(v) No transformation g_(d2) < g_(d1) and g_(v) < g_(h) Diagonalg_(d1) < g_(d2) and g_(h) < g_(v) Vertical flip g_(d1) < g_(d2) andg_(v) < g_(h) Rotation

In VVC, ALF filter parameters are signaled in adaption parameter set(APS). In one APS, a number of sets of luma filter coefficients andclipping value indexes may be used. For example, there may be 25 sets ofluma filters. In addition, a number of sets of chroma filtercoefficients and clipping value indexes could be signaled. In oneexample, there may be up to 8 sets of chroma filter coefficients andclipping value indexes that could be signaled. To reduce bits overhead,filter coefficients of different classification for luma component canbe merged. In slice header, the indices of the APSs used for the currentslice may be signaled. The signaling of ALF may be coding tree unit(CTU) based.

Clipping value indexes, which are decoded from the APS, allowdetermining clipping values using a table of clipping values for lumaand chroma. These clipping values may be dependent of the internal bitdepth. More precisely, the table of clipping values may be obtained bythe following formula:

AlfClip={round(2^(B-α*n)) for n∈[0 . . . N−1]}  (12)

with B equal to the internal bit depth, α is a pre-defined constantvalue equal to 2.35, and N equal to 4 which is the number of allowedclipping values in VVC in one embodiment. Table 3 shows the output ofequation (12):

TABLE 3 Specification AlfClip depending on bitDepth and clipIdx clipIdxbitDepth 0 1 2 3 8 255 50 10 2 9 511 100 20 4 10 1023 201 39 8 11 2047402 79 15 12 4095 803 158 31 13 8191 1607 315 62 14 16383 3214 630 12415 32767 6427 1261 247 16 65535 12855 2521 495

In one slice header example, up to 7 APS indices can be signaled tospecify the luma filter sets that are used for the current slice. Thefiltering process may be further controlled at the coding tree block(CTB) level. A flag may be signaled to indicate whether ALF is appliedto a luma CTB. In one example, a luma CTB can choose a filter set among16 fixed filter sets and the filter sets from APSs. A filter set indexis signaled for a luma CTB to indicate which filter set is applied. The16 fixed filter sets may be pre-defined and hard-coded in both theencoder and the decoder. For chroma component, an APS index is signaledin the slice header to indicate the chroma filter sets being used forthe current slice. At CTB level, a filter index is signaled for eachchroma CTB if there is more than one chroma filter set in the APS. Thefilter coefficients may be quantized with norm equal to 128. In order torestrict the multiplication complexity, a bitstream conformance isapplied so that the coefficient value of the non-central position may bein the range of −27 to 27−1, inclusive. The central position coefficientis not signaled in the bitstream and is considered as equal to 128.

In a VVC example, the syntaxes and semantics of clipping index andvalues may be defined as follows: alf_luma_clip_idx[sfIdx][j] specifiesthe clipping index of the clipping value to use before multiplying bythe j-th coefficient of the signalled luma filter indicated by sfIdx. Itmay be a requirement of bitstream conformance that the values ofalf_luma_clip_idx[sfIdx][j] with sfIdx=0 . . .alf_luma_num_filters_signalled_minus1 and j=0 . . . 11 shall be in therange of 0 to 3, inclusive. The luma filter clipping valuesAlfClipL[adaptation_parameter_set_id] with elementsAlfClipL[adaptation_parameter_set_id][filtIdx][j], with filtIdx=0 . . .NumAlfFilters−1 and j=0 . . . 11 are derived as specified in Table 3depending on bitDepth set equal to BitDepthY and clipIdx set equal toalf_luma_clip_idx[alf_luma_coeff_delta_idx[filtIdx]][j].alf_chroma_clip_idx[altIdx][j] specifies the clipping index of theclipping value to use before multiplying by the j-th coefficient of thealternative chroma filter with index altIdx. It is a requirement ofbitstream conformance that the values of alf_chroma_clip_idx[altIdx][j]with altIdx=0 . . . alf_chroma_num_alt_filters_minus1, j=0 . . . 5 shallbe in the range of 0 to 3, inclusive. The chroma filter clipping valuesAlfClipC[adaptation_parameter_set_id][altIdx] with elementsAlfClipC[adaptation_parameter_set_id][altIdx][j], with altIdx=0 . . .alf_chroma_num_alt_filters_minus1, j=0 . . . 5 are derived as specifiedin Table 3 depending on bitDepth set equal to BitDepthC and clipIdx setequal to alf_chroma_clip_idx[altIdx][j].

The filtering process may be performed in the following example. Atdecoder side, when ALF is enabled for a CTB, each sample R(i, j) withinthe CU is filtered, resulting in sample value R′(i, j):

R′(i,j)=R(i,j)+((Σ_(k≠0)Σ_(l≠0)f(k,l)×K(R(i+k,j+l)−R(i,j),c(k,l))+64)>>7)  (13)

where f(k, l) denotes the decoded filter coefficients, K(x, y) is theclipping function and c(k, l) denotes the decoded clipping parameters.The variable k and l vary between −L/2 and L/2 where L denotes thefilter length. The clipping function K(x, y)=min(y, max(−y, x)) whichcorresponds to the function Clip3 (−y, y, x). By incorporating thisclipping function, as first proposed in JVET-N0242, this loop filteringmethod becomes a non-linear process, as known as Non-Linear ALF. Theselected clipping values are coded in the “alf_data” syntax element byusing a Golomb encoding scheme corresponding to the index of theclipping value in Table 3. This encoding scheme may be the same as theencoding scheme for the filter index.

There may be a virtual boundary filtering process for line bufferreduction. To reduce the line buffer requirement of ALF, a modifiedblock classification and filtering may be applied for the samples nearhorizontal CTU boundaries. Accordingly, a virtual boundary may bedefined as a line by shifting the horizontal CTU boundary with “N”samples as shown in FIG. 20 . FIG. 20 shows an example of modified blockclassification at virtual boundaries. In this example, N is equal to 4for the luma component and 2 for the chroma component.

The modified block classification is applied for the Luma component asdepicted in FIG. 20 . For the 1D Laplacian gradient calculation of the4×4 block above the virtual boundary, only the samples above the virtualboundary are used. Similarly, for the 1D Laplacian gradient calculationof the 4×4 block below the virtual boundary, only the samples below thevirtual boundary are used. The quantization of activity value A isscaled by taking into account the reduced number of samples used in 1DLaplacian gradient calculation.

FIG. 21 shows an example of modified adaptive loop filtering for lumacomponent at virtual boundaries. For filtering processing, symmetricpadding operation at the virtual boundaries may be used for both lumaand chroma components. As shown in FIG. 21 , when the sample beingfiltered is located below the virtual boundary, the neighboring samplesthat are located above the virtual boundary are padded. Thecorresponding samples at the other sides may also be padded,symmetrically.

FIG. 22 shows an example of largest coding unit (LCU) aligned picturequadtree splitting. In order enhance coding efficiency, the coding unitsynchronous picture quadtree-based adaptive loop filter may be used. Theluma picture may be split into several multi-level quadtree partitions,and each partition boundary is aligned to the boundaries of the largestcoding units (LCUs). Each partition has its own filtering process andmay be referred to as a filter unit (FU). The two pass encoding flow mayinclude the following. At the first pass, the quadtree split pattern andthe best filter of each FU are decided. The filtering distortions areestimated by FFDE during the decision process. According to the decidedquadtree split pattern and the selected filters of all FUs, thereconstructed picture is filtered. At the second pass, the CUsynchronous ALF on/off control is performed. According to the ALF on/offresults, the first filtered picture is partially recovered by thereconstructed picture.

A top-down splitting strategy may be adopted to divide a picture intomulti-level quadtree partitions by using a rate-distortion criterion.Each partition may be referred to as a filter unit. The splittingprocess aligns quadtree partitions with LCU boundaries. The encodingorder of FUs follows the z-scan order. For example, in FIG. 22 , thepicture is split into 10 FUs, and the encoding order is FU0, FU1, FU2,FU3, FU4, FU5, FU6, FU7, FU8, and FU9.

FIG. 23 shows an example of quadtree split flags encoded in the z order.To indicate the picture quadtree split pattern, split flags are encodedand transmitted in z-order. FIG. 23 shows the quadtree split pattern incorrespondence with FIG. 22 . The filter of each FU is selected from twofilter sets based on the rate-distortion criterion. The first set has1/2-symmetric square-shaped and rhombus-shaped filters newly derived forthe current FU. The second set comes from time-delayed filter buffers;the time-delayed filter buffers store the filters previously derived forFUs of prior pictures. The filter with the minimum rate-distortion costof these two sets is chosen for the current FU. Similarly, if thecurrent FU is not the smallest FU and can be further split into 4children FUs, the rate-distortion costs of the 4 children FUs arecalculated. By comparing the rate-distortion cost of the split andnon-split cases recursively, the picture quadtree split pattern can bedecided. In one example, the maximum quadtree split level may be 2,which means the maximum number of FUs is 16. During the quadtree splitdecision, the correlation values for deriving Wiener coefficients of the16 FUs at the bottom quadtree level (smallest FUs) can be reused. Therest FUs can derive their Wiener filters from the correlations of the 16FUs at the bottom quadtree level. Therefore, there may be only one framebuffer access for deriving the filter coefficients of all FUs. After thequadtree split pattern is decided, to further reduce the filteringdistortion, the CU synchronous ALF on/off control is performed. Bycomparing the filtering distortion and non-filtering distortion, theleaf CU can explicitly switch ALF on/off in its local region. The codingefficiency may be further improved by redesigning the filtercoefficients according to the ALF on/off results. However, theredesigning process may need additional frame buffer accesses. In amodified encoder design, there may be no redesign process after the CUsynchronous ALF on/off decision in order to minimize the number of framebuffer accesses.

Cross-Component Adaptive Loop Filter (CC-ALF)

FIG. 24 shows an example of cross-component adaptive loop filter(CC-ALF) placement. CC-ALF may make use of luma sample values to refineeach chroma component. FIG. 24 illustrates the placement of CC-ALF withrespect to the other loop filters.

FIG. 25 shows an example of a diamond shaped filter. CC-ALF may operateby applying a linear, diamond shaped filter from FIG. 25 to the lumachannel for each chroma component. The filter coefficients aretransmitted in the APS, scaled by a factor of 210 in one example, androunded for fixed point representation. The application of the filtersis controlled on a variable block size and signaled by a context-codedflag received for each block of samples. The block size along with anCC-ALF enabling flag is received at the slice-level for each chromacomponent. In one example, the following block sizes (in chroma samples)were supported 16×16, 32×32, 64×64.

Example syntax for CC-ALF may include:

if ( slice_cross_component_alf_cb_enabled_flag )  alf_ctb_cross_component_cb_idc[ xCtb >> CtbLog2SizeY ][ yCtb >>CtbLog2SizeY ] ae(v)  if( slice_cross_component_alf_cb_enabled_flag = =0 || alf_ctb_cross_component_cb_idc[ x Ctb >> CtbLog2SizeY ][ yCtb >>CtbLog2SizeY ] == 0 )   if( slice_alf_chroma_idc = = 1 | |slice_alf_chroma_idc = = 3 ) {    alf_ctb_flag[ 1 ][ xCtb >>CtbLog2SizeY ][ yCtb >> CtbLog2SizeY ] ae(v)    if( alf_ctb_flag[ 1 ][xCtb >> CtbLog2SizeY ][ yCtb >> CtbLog2SizeY ]     &&aps_alf_chroma_num_alt_filters_minus1 > 0 )     alf_ctb_filter_alt_idx[0 ][ xCtb >> CtbLog2SizeY ][ yCtb >> CtbLog2SizeY ] ae(v)   }  if (slice_cross_component_alf_cr_enabled_flag )  alf_ctb_cross_component_cr_idc[ xCtb >> CtbLog2SizeY ][ yCtb >>CtbLog2SizeY ] ae(v)  if( slice_cross_component_alf_cr_enabled_flag = =0 || alf_ctb_cross_component_cr_idc[ xC tb >> CtbLog2SizeY ][ yCtb >>CtbLog2SizeY ] == 0 )   if( slice_alf_chroma_idc = = 2 | |slice_alf_chroma_idc = = 3 ) {    alf_ctb_flag[ 2 ][ xCtb >>CtbLog2SizeY ][ yCtb >> CtbLog2SizeY ] ae(v)    if( alf_ctb_flag[ 2 ][xCtb >> CtbLog2SizeY ][ yCtb >> CtbLog2SizeY ]     &&aps_alf_chroma_num_alt_filters_minus1 > 0 )     alf_ctb_filter_alt_idx[1 ][ xCtb >> CtbLog2SizeY ][ yCtb >> CtbLog2SizeY ] ae(v)   }The semantics of CC-ALF related syntaxes may include:alf_ctb_cross_component_cb_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]equal to 0 indicates that the cross component Cb filter is not appliedto block of Cb colour component samples at luma location (xCtb, yCtb).alf_cross_component_cb_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] notequal to 0 indicates that thealf_cross_component_cb_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]-thcross component Cb filter is applied to the block of Cb colour componentsamples at luma location (xCtb, yCtb)alf_ctb_cross_component_cr_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]equal to 0 indicates that the cross component Cr filter is not appliedto block of Cr colour component samples at luma location (xCtb, yCtb).alf_cross_component_cr_idc[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY] notequal to 0 indicates that thealf_cross_component_cr_idd[xCtb>>CtbLog2SizeY][yCtb>>CtbLog2SizeY]-thcross component Cr filter is applied to the block of Cr colour componentsamples at luma location (xCtb, yCtb)

Chroma Sampling Formats

FIG. 26 shows an example location of chroma samples relative to lumasamples. FIG. 26 illustrates the indicated relative position of thetop-left chroma sample when chroma_format_idc is equal to 1 (4:2:0chroma format), and chroma_sample_loc_type_top_field orchroma_sample_loc_type_bottom_field is equal to the value of a variableChromaLocType. The region represented by the top-left 4:2:0 chromasample (depicted as a large square with a large dot at its center) isshown relative to the region represented by the top-left luma sample(depicted as a small square with a small dot at its center). The regionsrepresented by neighboring luma samples are depicted as small shadedgray squares with small shaded grey dots at their centers.

Directional Enhancement Feature

One objective of the in-loop constrained directional enhancement filter(CDEF) is to filter out coding artifacts while retaining the details ofthe image. In HEVC, the Sample Adaptive Offset (SAO) algorithm mayachieve a similar objective by defining signal offsets for differentclasses of pixels. Unlike SAO, CDEF is a non-linear spatial filter. Thedesign of the filter has been constrained to be easily vectorizable(i.e. implementable with SIMD operations), which may not be the case forother non-linear filters like the median filter and the bilateralfilter. The CDEF design originates from the following observations. Theamount of ringing artifacts in a coded image tends to be roughlyproportional to the quantization step size. The amount of detail is aproperty of the input image, but the smallest detail retained in thequantized image tends to also be proportional to the quantization stepsize. For a given quantization step size, the amplitude of the ringingis generally less than the amplitude of the details.

CDEF works by identifying the direction of each block and thenadaptively filtering along the identified direction and to a lesserdegree along directions rotated 45 degrees from the identifieddirection. The filter strengths are signaled explicitly, which allows ahigh degree of control over the blurring. An efficient encoder search isdesigned for the filter strengths. CDEF is based on two previouslyproposed in-loop filters and the combined filter was adopted for theemerging AV1 codec.

FIG. 27 shows an example of direction search. The direction searchoperates on the reconstructed pixels, just after the deblocking filter.Since those pixels are available to the decoder, the directions requireno signaling. The search operates on 8×8 blocks, which are small enoughto adequately handle non-straight edges, while being large enough toreliably estimate directions when applied to a quantized image. Having aconstant direction over an 8×8 region also makes vectorization of thefilter easier. For each block we determine the direction that bestmatches the pattern in the block by minimizing the sum of squareddifferences (SSD) between the quantized block and the closest perfectlydirectional block. A perfectly directional block is a block where all ofthe pixels along a line in one direction have the same value. FIG. 27 isone example of direction search for an 8×8 block.

There may be a non-linear low-pass directional filter. One reason foridentifying the direction is to align the filter taps along thatdirection to reduce ringing while preserving the directional edges orpatterns. However, directional filtering alone sometimes cannotsufficiently reduce ringing. It may also be desired to use filter tapson pixels that do not lie along the main direction. To reduce the riskof blurring, these extra taps are treated more conservatively. For thisreason, CDEF defines primary taps and secondary taps. The complete 2-DCDEF filter may be expressed as

$\begin{matrix}{{{y\left( {i,j} \right)} = {{x\left( {i,j} \right)} + {{round}\left( {{\sum\limits_{m,n}{w_{d,m,n}^{(p)}{f\left( {{{x\left( {m,n} \right)} - {x\left( {i,j} \right)}},S^{(p)},D} \right)}}} + {\sum\limits_{m,n}{w_{d,m,n}^{(s)}{f\left( {{{x\left( {m,n} \right)} - {x\left( {i,j} \right)}},S^{(s)},D} \right)}}}} \right)}}},} & (14)\end{matrix}$

where D is the damping parameter, S^((p)) and S^((s)) are the strengthsof the primary and secondary taps, respectively, and round(⋅) roundsties away from zero, w_(k) are the filter weights and f(d, S, D) is aconstraint function operating on the difference between the filteredpixel and each of the neighboring pixels. For small differences, f(d, S,D)=d, making the filter behave like a linear filter. When the differenceis large, f(d, S, D)=0, which effectively ignores the filter tap.

Loop Restoration

A set of in-loop restoration schemes are proposed for use in videocoding post deblocking, to generally denoise and enhance the quality ofedges, beyond the traditional deblocking operation. These schemes areswitchable within a frame per suitably sized tile. The specific schemesdescribed are based on separable symmetric Wiener filters and dualself-guided filters with subspace projection. Because content statisticscan vary substantially within a frame, these tools are integrated withina switchable framework where different tools can be triggered indifferent regions of the frame.

There may be a separable symmetric wiener filter used as a restorationtool. Every pixel in a degraded frame could be reconstructed as anon-causal filtered version of the pixels within a w×w window around itwhere w=2r+1 is odd for integer r. If the 2D filter taps are denoted bya w2×1 element vector F in column-vectorized form, a straightforwardLMMSE optimization leads to filter parameters being given by F=H−1 M,where H=E[XXT] is the autocovariance of x, the column-vectorized versionof the w2 samples in the w×w window around a pixel, and M=E[YXT] is thecross correlation of x with the scalar source sample y, to be estimated.The encoder can estimate H and M from realizations in the deblockedframe and the source and send the resultant filter F to the decoder.However, that would not only incur a substantial bit rate cost intransmitting w2 taps, but also non-separable filtering will makedecoding prohibitively complex. Therefore, several additionalconstraints are imposed on the nature of F. First, F is constrained tobe separable so that the filtering can be implemented as separablehorizontal and vertical w-tap convolutions. Second, each of thehorizontal and vertical filters are constrained to be symmetric. Third,the sum of both the horizontal and vertical filter coefficients isassumed to sum to 1.

There may be dual self-guided filtering with subspace projection forimage filtering where a local linear model:

y=Fx+G  (15)

which is used to compute the filtered output y from an unfiltered samplex, where F and G are determined based on the statistics of the degradedimage and a guidance image in the neighborhood of the filtered pixel. Ifthe guide image is the same as the degraded image, the resultantso-called self-guided filtering has the effect of edge preservingsmoothing. The specific form of self-guided filtering we propose dependson two parameters: a radius r and a noise parameter e, and is enumeratedas follows:

-   -   1. Obtain mean μ and variance σ² of pixels in a (2r+1)×(2r+1)        window around every pixel. This can be implemented efficiently        with box filtering based on integral imaging.    -   2. Compute for every pixel: f=σ²/(σ²+e); g=(1−f)μ    -   3. Compute F and G for every pixel as averages off and g values        in a 3×3 window around the pixel for use.        Filtering may be controlled by r and e, where a higher r implies        a higher spatial variance and a higher e implies a higher range        variance.

FIG. 28 shows an example of subspace projection. The principle ofsubspace projection is illustrated diagrammatically in FIG. 28 . Eventhough none of the cheap restorations X1, X2 are close to the source Y,appropriate multipliers {α, β} can bring them much closer to the sourceas long as they are moving somewhat in the right direction.

Cross-Component Sample Offset (CCSO)

A loop filtering approach may include Cross-Component Sample Offset(CCSO) to reduce distortion of reconstructed samples. In CCSO, givenprocessed input reconstructed samples of a first color component, anon-linear mapping is used to derive output offset, and the outputoffset is added on the reconstruction sample of another color componentin the filtering process of the proposed CCSO.

FIG. 29 shows an example of a filter support area. The inputreconstructed samples are from a first color component located in filtersupport area. As shown in FIG. 29 , the filter support area includesfour reconstructed samples: p0, p1, p2, p3. The four input reconstructedsamples follow a cross-shape in vertical and horizontal direction. Thecenter sample (denoted by c) in the first color component and the sampleto be filtered in the second color component are co-located. Whenprocessing the input reconstructed samples, following steps are applied:

-   -   Step 1: The delta value between p0-p3 and c are computed first,        denoted as m0, m1, m2, and m3.    -   Step 2: The delta value m0-m3 are further quantized, the        quantized values are denoted as d0, d1, d2, d3. The quantized        value can be −1, 0, 1 based on the following quantization        process:

a. d=−1, if m<−N;  (16)

b. d=0, if −N<=m<=N;  (17)

c. d=1, if m>N.  (18)

where N is called quantization step size, example values of N are 4, 8,12, 16.

Variables d0-d3 may be used to identify one combination of thenon-linear mapping. In this example, CCSO has four filter taps d0-d3,and each filter tap may have one of the three quantized values, so thereare 3{circumflex over ( )}4=81 combinations in total. Table 4 (below)shows the 81 example combinations, the last column represents the outputoffset value for each combination. Example offset values are integers,such as 0, 1, −1, 3, −3, 5, −5, −7.

TABLE 4 Sample combinations identified by d0-d3 Combination d0 d1 d2 d3Offset 0 −1 −1 −1 −1 s0 1 −1 −1 −1 0 s1 2 −1 −1 −1 1 s2 3 −1 −1 0 −1 s34 −1 −1 0 0 s4 5 −1 −1 0 1 s5 6 −1 −1 1 −1 s6 7 −1 −1 1 0 s7 8 −1 −1 1 1s8 9 −1 0 −1 −1 s9 10 −1 0 −1 0 s10 11 −1 0 −1 1 s11 12 −1 0 0 −1 s12 13−1 0 0 0 s13 14 −1 0 0 1 s14 15 −1 0 1 −1 s15 16 −1 0 1 0 s16 17 −1 0 11 s17 18 −1 1 −1 −1 s18 19 −1 1 −1 0 s19 20 −1 1 −1 1 s20 21 −1 1 0 −1s21 22 −1 1 0 0 s22 23 −1 1 0 1 s23 24 −1 1 1 −1 s24 25 −1 1 1 0 s25 26−1 1 1 1 s26 27 0 −1 −1 −1 s27 28 0 −1 −1 0 s28 29 0 −1 −1 1 s29 30 0 −10 −1 s30 31 0 −1 0 0 s31 32 0 −1 0 1 s32 33 0 −1 1 −1 s33 34 0 −1 1 0s34 35 0 −1 1 1 s35 36 0 0 −1 −1 s36 37 0 0 −1 0 s37 38 0 0 −1 1 s38 390 0 0 −1 s39 40 0 0 0 0 s40 41 0 0 0 1 s41 42 0 0 1 −1 s42 43 0 0 1 0s43 44 0 0 1 1 s44 45 0 1 −1 −1 s45 46 0 1 −1 0 s46 47 0 1 −1 1 s47 48 01 0 −1 s48 49 0 1 0 0 s49 50 0 1 0 1 s50 51 0 1 1 −1 s51 52 0 1 1 0 s5253 0 1 1 1 s53 54 1 −1 −1 −1 s54 55 1 −1 −1 0 s55 56 1 −1 −1 1 s56 57 1−1 0 −1 s57 58 1 −1 0 0 s58 59 1 −1 0 1 s59 60 1 −1 1 −1 s60 61 1 −1 1 0s61 62 1 −1 1 1 s62 63 1 0 −1 −1 s63 64 1 0 −1 0 s64 65 1 0 −1 1 s65 661 0 0 −1 s66 67 1 0 0 0 s67 68 1 0 0 1 s68 69 1 0 1 −1 s69 70 1 0 1 0s70 71 1 0 1 1 s71 72 1 1 −1 −1 s72 73 1 1 −1 0 s73 74 1 1 −1 1 s74 75 11 0 −1 s75 76 1 1 0 0 s76 77 1 1 0 1 s77 78 1 1 1 −1 s78 79 1 1 1 0 s7980 1 1 1 1 s80

The final filtering process of CCSO is applied as follows:

f′=clip(f+s),  (19)

where f is the reconstructed sample to be filtered, and s is the outputoffset value retrieved from Table 4, the filtered sample value f′ isfurther clipped into the range associated with bit-depth.

Local sample offset (LSO) is another example offset embodiment. In LSO,the similar filtering approach in CCSO is applied, but the outputoffsets are applied on a color component that is the same colorcomponent of which the reconstructed samples are used as the input tothe filtering process.

In an alternative embodiment, a simplified CCSO design may be adoptedinto the reference software of AV2, i.e., AVM for CWG-B022.

FIG. 30 shows an example loop filter pipeline. CCSO is a loop filterprocess that is performed in parallel to CDEF in the loop filterpipeline, i.e., the input is same with CDEF, and the output is appliedon CDEF filtered samples, as illustrated in FIG. 30 . It is noted thatCCSO may be applied only on chroma color components.

FIG. 31 shows example inputs of cross-component sample offset (CCSO).The CCSO filter is applied on chroma reconstructed sample, denoted asrc. The co-located luma reconstructed sample of rc is denoted as rl. Anexample of CCSO filter is shown in FIG. 31 . In CCSO, a set of 3-tapfilters are used. The input luma reconstructed samples located at thethree filter taps include rl in the center, and two neighboring samplesp₀ and p₁.

Given p_(i) and rl, where i=0, 1, following steps are applied to processthe input samples:

The delta value between p_(i) and rl is computed first, denoted as m_(i)

The delta value m_(i) is quantized as d_(i), using the followingquantization process:

-   -   d_(i) is set equal to −1 when m is less than −Q_(CCSO)    -   d_(i) is set equal to 0 when m is between −Q_(CCSO) and        Q_(CCSO), inclusive    -   d_(i) is set equal to 1 when m is greater than Q_(CCSO)        In the above steps, Q_(CCSO) is called quantization step size,        Q_(CCSO) can be 8, 16, 32, 64.

After d₀ and d₁ are calculated, the offset value (denoted as s) isderived using the look-up table (LUT) of CCSO. The LUT of CCSO is shownin Table 5. Each combination of d₀ and d₁ is used to identify a row inthe LUT to retrieve the offset value. The offset values are integersincluding 0, 1, −1, 3, −3, 5, −5 and −7.

TABLE 5 The look-up table (LUT) used in CCSO combination index d0 d1offset 0 −1 −1 s0 1 −1 0 s1 2 −1 1 s2 3 0 −1 s3 4 0 0 s4 5 0 1 s5 6 1 −1s6 7 1 0 s7 8 1 1 s8

Finally, the derived offset of CCSO is applied on chroma colourcomponent as follows:

rc′=clip(rc+s),  (20)

where rc is the reconstructed sample to be filtered by CCSO, and s isthe derived offset value retrieved from the LUT, the filtered samplevalue rc′ is further clipped into the range specified by the bit depth.

FIG. 32 shows example filter shapes in cross-component sample offset(CCSO). In CCSO, there are six optional filter shapes, denoted as f_(i),i=1 . . . 6, as shown in FIG. 32 . These six filter shapes areswitchable at frame level, and the selection is signaled by a syntaxext_filter_support using 3-bit fixed length code.

Signaling of cross-component sample offset (CCSO) may be performed atboth frame-level and block-level. At frame-level, the signals mayinclude:

A 1-bit flag indicating whether CCSO is applied

A 3-bit syntax ext_filter_support indicating the selection of CCSOfilter shape

A 2-bit index indicating the selection of quantization step size

Nine 3-bit offset values used in the LUT

At 128×128 chroma block-level, a flag is signaled to indicate whetherthe CCSO filter is enabled or not.

Sample Adaptive Offset (SAO)

In HEVC, Sample Adaptive Offset (SAO) is applied to the reconstructionsignal after the deblocking filter by using the offset values given inthe slice header. For luma samples, the encoder decides on whether theSAO is applied for current slice. If SAO is enabled, the current pictureallows recursive splitting into four sub-regions and each region canselect one of six SAO types as shown in Table 6. SAO classifiesreconstructed pixels into categories and reduces the distortion byadding an offset to pixels of each category in current region. Edgeproperties are used for pixel classification in SAO types 1-4, and pixelintensity is used for pixel classification in SAO types 5-6.

TABLE 6 Specification of SAO type sample adaptive offset Number of SAOtype type to be used categories 0 None 0 1 1-D 0-degree pattern edgeoffset 4 2 1-D 90-degree pattern edge offset 4 3 1-D 135-degree patternedge 4 offset 4 1-D 45-degree pattern edge offset 4 5 central bands bandoffset 16 6 side bands band offset 16

Band offset (BO) classifies all pixels of a region into multiple bandswhere each band contains pixels in the same intensity interval. Theintensity range is equally divided into 32 intervals from zero to themaximum intensity value (e.g. 255 for 8-bit pixels), and each intervalhas an offset. Next, the 32 bands are divided into two groups. One groupconsists of the central 16 bands, while the other group consists of therest 16 bands. Only offsets in one group are transmitted. Regarding thepixel classification operation in BO, the five most significant bits ofeach pixel can be directly used as the band index.

FIG. 33 shows example pixel patterns. Edge offset (EO) uses four 1-D3-pixel patterns for pixel classification with consideration of edgedirectional information, as shown in FIG. 33 . Each region of a picturecan select one pattern to classify pixels into multiple categories bycomparing each pixel with its two neighboring pixels. The selection willbe sent in bit-stream as side information. Table 7 shows the pixelclassification rule for EO.

TABLE 7 Pixel classification rule for edge offset (EO) CategoryCondition 1 c < 2 neighbors 2 c < 1 neighbor && c == 1 neighbor 3 c > 1neighbor && c == 1 neighbor 4 c > 2 neighbors 0 None of the above

The SAO on the decoder side may be operated LCU-independently so thatthe line buffers can be saved. In order to achieve this, pixels of thetop and bottom rows in each LCU may not be SAO processed when the90-degree, 135-degree, and 45-degree classification patterns are chosen.Pixels of the leftmost and rightmost columns in each LCU may not be SAOprocessed when the 0-degree, 135-degree, and 45-degree patterns arechosen.

The following Table 8 illustrates example syntaxes that may need to besignaled for a CTU if the parameters are not merged from neighboringCTU:

TABLE 8 Sample adaptive offset VLC syntax Descriptor sao_offset_vlc( rx,ry, cIdx ) {  sao_type_idx[ cIdx ][ rx ][ ry ] ue(v)  if( sao_type_idx[cIdx ][ rx ][ ry ] = =5 ) {   sao_band_position[ cIdx ][ rx ][ ry ] u(5)  for( i = 0; i < 4; i++ )    sao_offset[ cIdx ][ rx ][ ry ][ i ] se(v) } else if( sao_type_idx[ cIdx ][ rx ][ ry ] != 0 )   for( i = 0; i < 4;i++ )    sao_offset[ cIdx ][ rx ][ ry ][ i ] ue(v) }

Cross-Component Sample Offset (CCSO) and Local Sample Offset (LSO) canutilize the value of pixel to be filtered for selecting offset value onone color component. However, further extending those inputs for offsetselection may significantly increase the overhead of signaling of CCSOand LSO, which may limit/reduce the coding performance, especially forsmaller resolution sequences.

As described, CCSO is defined as a filtering process which uses thereconstructed samples of a first color component as input (e.g., Y or Cbor Cr), and the output is applied on a second color component which is adifferent color component of the first color component. An examplefilter shape of CCSO is shown in FIG. 29 . The LSO is a filteringprocess which uses the reconstructed samples of a first color componentas input (e.g., Y or Cb or Cr), and the output is applied on the samefirst color component. Accordingly, a difference between LSO and CCSO isdifferent inputs.

As described below and illustrated in FIG. 34 , a generalized design forCCSO and LSO is presented by not only considering the delta valuebetween neighboring samples of collocated (or current) sample, asconsidered in CCSO and LSO, but also considering the level value of thecollocated (or current) sample itself.

FIG. 34 shows a flow chart of a method according to an exampleembodiment of the disclosure. In block 3402, coded information for areconstructed sample of a current component in a current picture from acoded video bitstream is decoded. The coded information indicates asample offset filter to be applied to the reconstructed sample. Thesample offset filter may include two types of offset values in oneexample, a gradient offset (GO) and a band offset (BO). In block 3404,the offset type is selected to be used with the sample offset filter. Inblock 3406, an output value of the sample offset filter is determinedbased on the first reconstructed samples and the selected offset type.In block 3408, a filtered sample value of the reconstructed sample ofthe current component is determined based on the reconstructed sampleand the output value of the sample offset filter. Further embodimentsare described below.

A generalized sample offset (GSO) method may include two types of offsetvalues for CCSO and LSO, including a gradient offset (GO) and bandoffset (BO). The selection of the offset type can be either signaled orimplicitly derived.

In one embodiment, the gradient offset may be an offset derived usingthe delta value between neighboring samples and a co-located sample of adifferent color component (in the case of CCSO) or the delta valuebetween neighboring samples and the current sample to be filtered (inthe case of CCSO or LSO).

In one embodiment, the band offset may be an offset derived using thevalue of co-located sample of a different color component or the currentsample to be filtered. The band may be used to determine the offsetvalue. In one example, the value of co-located sample of a differentcolor component or the current sample to be filtered may be denoted as avariable v, and the BO value is derived using v>>s, where >> indicatesright shift operation, s is a pre-defined value specifying the intervalof sample values that use the same band offset. In one example, thevalue of s can vary for different color components. In another example,the value of co-located sample of a different color component or thecurrent sample to be filtered is denoted as a variable v, and a bandindex bi is derived using a predefined lookup table, wherein the inputof the lookup table is v and the output value is a band index bi, andthe BO value is derived using the band index bi.

In one embodiment, when a combination of GO and BO is applied (e.g. usedat the same time), the offset is derived using both 1) the delta valuebetween neighboring samples and co-located sample of a different colorcomponent (in the case of CCSO) or the delta value between neighboringsamples and the current sample to be filtered (in the case of CCSO orLSO); and 2) the value of co-located sample of a different colorcomponent or the current sample to be filtered.

In one embodiment, the application of GO or BO is signaled. Thissignaling may be applied in high-level syntax. As a few examples, thesignaling may include VPS, PPS, SPS, Slice header, picture header, frameheader, superblock header, CTU header, tile header.

In another embodiment, whether GO or BO is signaled in at block level,the said block level includes, but is not limited to coding unit (block)level, prediction block level, transform block level, or filtering unitlevel. This example includes signaling at the block level to identify GOor BO.

In another embodiment, GO or BO is signaled using a flag. A flag isfirst signaled to indicate whether LSO and/or CCSO is applied for one ormultiple color components, then another flag is signaled to indicatewhether GO or BO is applied. For example, a flag is first signaled toindicate whether LSO and/or CCSO is applied for one or multiple colorcomponents, then another flag is signaled to indicate whether GO isapplied jointly with BO, where BO is always applied regardless whetherGO is applied or not. In another example, a flag is first signaled toindicate whether LSO and/or CCSO is applied for one or multiple colorcomponents, then another flag is signaled to indicate whether BO isapplied jointly with GO, where GO is always applied regardless whetherBO is applied or not.

In some embodiments, the signal may be derived for determining whetherto use GO or BO or a combination of them. It may be implicitly derivedusing coded information, including but not limited to reconstructedsample of current color component and/or a different color component,whether the current block is intra or inter coded, whether the currentpicture is a key (or intra) picture, whether the current sample (orblock) is coded by a specific prediction mode (such as a specific intraor inter prediction mode, a transform selection mode, the quantizationparameter.

As described, LSO may be similar to CCSO, but the output offsets areapplied on a color component that is the same as the color component ofwhich the reconstructed samples are used as the input to the filteringprocess. GSO is a generalized design that considers two types of offsetvalues, including a gradient offset (GO), which considers a delta valuebetween neighboring samples of a collocated or current sample, and aband offset (BO), which considers the level value of the current sampleitself.

Additionally, the signaling aspects CCSO, LSO, and GSO may becategorized into a frame level and a block level. At the frame level,the enabling of CCSO, LSO, and/or GSO may be signaled (such as by usinga 1-bit flag), and/or the offset value(s) of the LUT may be signaled(such as by using three-bits each). At the block level, for an M×Nblock, a flag is signaled to indicate the enabling of CCSO, LSO, and/orGSO for a current block. In various embodiments, the values of M and Neach may include, but are not limited to, 16, 32, 64, 128, or 256. Asused herein, the term block refers to a region of the frame.

The following describes adaptive application of GSO.

As described, CCSO is defined as a filtering process which uses thereconstructed samples of a first color component as input (e.g., Y or Cbor Cr), and the output is applied on a second color component that is adifferent color component than the first color component. An examplefilter shape of CCSO is shown in FIG. 29 . In addition, LSO is afiltering process which uses the reconstructed samples of a first colorcomponent as input (e.g., Y or Cb or Cr), and the output is applied onthe same first color component. GSO is a filtering process which can beconsidered as a generalized design for CCSO and LSO and utilizes thedelta value between neighboring samples of a collocated (or current)sample, as in CCSO and LSO, and also considers the level value of thecurrent sample. Two types of offset values are used in GSO, namely:Gradient offset (GO), which corresponds to the delta value betweenneighboring samples of a collocated or current sample, and a Band offset(BO), which corresponding to the level value of the current sampleitself.

FIG. 35 shows a flow chart of a method 3500 according to an exampleembodiment of the disclosure. The example method 3500 may be performedby an apparatus configured to decode a video stream, such as the videodecoder (510) or the video decoder (810) described above. At least someof the actions in the method of FIG. 35 may be performed by a loopfilter, such as the loop filter (556) in FIG. 5 .

At block 3502, a coded video stream (e.g., a bitstream) is received. Thecoded video stream includes a syntax element that indicates whether asample offset filtering process is applied to a frame in the coded videostream at a block level. At block 3504, at least one of: a GSO, a LSO,or a CCSO is determined to be enabled for the frame at the block levelbased on the syntax element being a predefined value. The predefinedvalue may be one of a plurality of predefined values. Each of theplurality of predefined values may indicate whether a particular sampleoffset process (GSO, LSO, or CCSO), or a particular combination of twoor more sample offset processes (two or more of GSO, LSO, CCSO) isenabled. Accordingly, in some embodiments, at block 3504, at least theGSO is determined to be enabled. In addition or alternatively, at leastthe LSO is determined to be enabled. In addition or alternatively, atleast the CCSO is determined to be enabled. At block 3506, the codedvideo stream may be decoded by applying the at least one of the GSO, theLSO, or the CCSO at the block level. For example, the at least one ofthe GSO, the LSO, or the CCSO that is applied at block 3506 maycorrespond to, or be based on, the GSO, the LSO, and/or the CCSO that isdetermined to be enabled at block 3504. That is, if GSO is determined tobe enabled at block 3504, then GSO may be applied at block 3506; if LSOis determined to be enabled at block 3504, then LSO may be applied atblock 3506; and if CCSO is determined to be enabled at block 3504, thenCCSO may be applied at block 3506. For at least some embodiments of themethod 3500, a block size of the frame in the coded video stream isdifferent for a luma component and a chroma component in thecorresponding frame.

In some embodiments, applying the at least one of the GSO, the LSO, orthe CCSO at block 3506 includes applying the GSO, where a first blocksize of a luma component is the same as or smaller than a second blocksize of the chroma component. For example, the granularity ofapplication of GSO is finer for the luma component compared to thechroma component. As an example, M×N used for luma GSO is 128×128 orsmaller when that of chroma is 128×128. The values of M and N mayinclude but are not limited to 16, 32, 64, 128, or 256.

In some embodiments, the method 3500 may further include receiving asignal indicating a first block-level flag for a luma component having afirst block size that is the same as or smaller than a second block sizeof a chroma component when a second block-level flag for the chromacomponent having the second block size is signaled. For example, thegranularity of signaling a block-level flag is finer for a lumacomponent compared to a chroma component. As an example, the block levelflag is signaled for block sizes 128×128 or smaller when that of chromacomponent is signaled for 128×128 size blocks.

In some embodiments, a block-level flag indicating whether one of CCSO,LSO, or GSO is enabled or disabled, such as for application to a block,may also indicate whether another of CCSO, LSO, or GSO is enabled ordisabled for the block. For example, a block-level flag indicating thatCCSO is enabled for the chroma component of a block may also indicatethat LSO is enabled for the luma component of the block. Likewise, ablock-level flag indicating that LSO is enabled for the luma componentof a block may also indicate that CCSO is enabled for the chromacomponent of the block. As an example, a block-level flag indicatingwhether CCSO is enabled or applied for a block may depend on a blocklevel flag indicating whether LSO is enabled or applied for the block,and/or a block-level flag indicating whether LSO is applied for a blockmay depend on a block level flag indicating whether CCSO is applied forthe block. In addition or alternatively, a block-level flag indicatingwhether CCSO or LSO is applied for a block can be used as a context forsignaling a block-level flag to indicate whether LSO or CCSO,respectively, is applied for the block.

In some embodiments, the method 3500 may further include receiving, in ahigh-level syntax, a signal indicating a granularity of at least one ofa chroma component or a luma component for application of the GSO,wherein the high-level syntax comprises: a video parameter set (VPS), apicture parameter set (PPS), a sequence parameter setting (SPS), anadaptation parameter set (APS), a frame header, a slice header, apicture header, a tile header, a superblock header, or a coding treeunit (CTU) header. For example, the granularity of application of GSOfor the luma component and/or for the chroma component can be signaledin a high-level syntax that includes, but not limited to, VPS, PPS, SPS,APS, frame header, slice header, picture header, tile header, superblockheader, and/or CTU header.

In some embodiments, the syntax element is or includes a high-levelsyntax, the GSO is enabled by the high-level syntax, and method 3500 mayfurther include receiving a signal comprising an additional high-levelsyntax to indicate a maximum number of bands used for a band offset. Forexample, when GSO is enabled by a high-level syntax, an additionalhigh-level syntax is signaled to indicate the maximum number of bandsused for BO. For some of these embodiments, the high-level syntaxincludes, but is not limited to, VPS, PPS, SPS, APS, frame header, sliceheader, picture header, tile header, superblock header, and/or CTUheader.

In some embodiments, a block-level flag enables the GSO for a block, andthe method 3500 may further include receiving a signal comprising anadditional high-level syntax to indicate a number of bands used for aband offset (BO) in the block. For example, when the block level flagenables GSO for a block, an additional block level syntax is signaled toindicate the number of bands used for BO in that block. In some of theseembodiments, the number of bands for the band offset in the block isless than a number of bands signaled at a frame level. For example, thenumber of bands used for BO at block level is always less than or equalto maximum number of bands that was signaled at frame level. In additionor alternatively, the syntax element is or includes a high-level syntax,and the method 3500 may further include: receiving a signal comprising aflag to indicate whether a single band or a maximum number of bandsspecified in the high-level syntax is applied for a current block. Forexample, a flag is signalled to indicate whether a single band or themaximum number of bands specified in high-level syntax is applied forthe current block.

Embodiments in the disclosure may be used separately or combined in anyorder. Further, each of the methods (or embodiments), an encoder, and adecoder may be implemented by processing circuitry (e.g., one or moreprocessors or one or more integrated circuits). In one example, the oneor more processors execute a program that is stored in a non-transitorycomputer-readable medium. The term block may include a prediction block,a coding block, or a coding unit, i.e. CU. Embodiments in the disclosuremay be applied to a luma block or a chroma block.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 36 shows a computersystem (3600) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 36 for computer system (3600) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (3600).

Computer system (3600) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (3601), mouse (3602), trackpad (3603), touchscreen (3610), data-glove (not shown), joystick (3605), microphone(3606), scanner (3607), camera (3608).

Computer system (3600) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (3610), data-glove (not shown), or joystick (3605), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (3609), headphones(not depicted)), visual output devices (such as screens (3610) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (3600) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(3620) with CD/DVD or the like media (3621), thumb-drive (3622),removable hard drive or solid state drive (3623), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (3600) can also include an interface (3654) to one ormore communication networks (3655). Networks can for example bewireless, wireline, optical. Networks can further be local, wide-area,metropolitan, vehicular and industrial, real-time, delay-tolerant, andso on. Examples of networks include local area networks such asEthernet, wireless LANs, cellular networks to include GSM, 3G, 4G, 5G,LTE and the like, TV wireline or wireless wide area digital networks toinclude cable TV, satellite TV, and terrestrial broadcast TV, vehicularand industrial to include CAN bus, and so forth. Certain networkscommonly require external network interface adapters that attached tocertain general-purpose data ports or peripheral buses (3649) (such as,for example USB ports of the computer system (3600)); others arecommonly integrated into the core of the computer system (3600) byattachment to a system bus as described below (for example Ethernetinterface into a PC computer system or cellular network interface into asmartphone computer system). Using any of these networks, computersystem (3600) can communicate with other entities. Such communicationcan be uni-directional, receive only (for example, broadcast TV),uni-directional send-only (for example CANbus to certain CANbusdevices), or bi-directional, for example to other computer systems usinglocal or wide area digital networks. Certain protocols and protocolstacks can be used on each of those networks and network interfaces asdescribed above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (3640) of thecomputer system (3600).

The core (3640) can include one or more Central Processing Units (CPU)(3641), Graphics Processing Units (GPU) (3642), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(3643), hardware accelerators for certain tasks (3644), graphicsadapters (3650), and so forth. These devices, along with Read-onlymemory (ROM) (3645), Random-access memory (3646), internal mass storagesuch as internal non-user accessible hard drives, SSDs, and the like(3647), may be connected through a system bus (3648). In some computersystems, the system bus (3648) can be accessible in the form of one ormore physical plugs to enable extensions by additional CPUs, GPU, andthe like. The peripheral devices can be attached either directly to thecore's system bus (3648), or through a peripheral bus (3649). In anexample, the screen (3610) can be connected to the graphics adapter(3650). Architectures for a peripheral bus include PCI, USB, and thelike.

CPUs (3641), GPUs (3642), FPGAs (3643), and accelerators (3644) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(3645) or RAM (3646). Transitional data can also be stored in RAM(3646), whereas permanent data can be stored for example, in theinternal mass storage (3647). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (3641), GPU (3642), massstorage (3647), ROM (3645), RAM (3646), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As a non-limiting example, the computer system having architecture(3600), and specifically the core (3640) can provide functionality as aresult of processor(s) (including CPUs, GPUs, FPGA, accelerators, andthe like) executing software embodied in one or more tangible,computer-readable media. Such computer-readable media can be mediaassociated with user-accessible mass storage as introduced above, aswell as certain storage of the core (3640) that are of non-transitorynature, such as core-internal mass storage (3647) or ROM (3645). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (3640). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(3640) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (3646) and modifying such data structuresaccording to the processes defined by the software. In addition, or asan alternative, the computer system can provide functionality as aresult of logic hardwired or otherwise embodied in a circuit (forexample: accelerator (3644)), which can operate in place of or togetherwith software to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

APPENDIX A: ACRONYMS ALF: Adaptive Loop Filter AMVP: Advanced MotionVector Prediction APS: Adaptation Parameter Set ASIC:Application-Specific Integrated Circuit AV1: AOMedia Video 1 AV2:AOMedia Video 2

BCW: Bi-prediction with CU-level Weights

BM: Bilateral Matching

BMS: benchmark set

CANBus: Controller Area Network Bus CC-ALF: Cross-Component AdaptiveLoop Filter CCSO: Cross-Component Sample Offset CD: Compact Disc CDEF:Constrained Directional Enhancement Filter CDF: Cumulative DensityFunction

CfL: Chroma from LumaCIIP: Combined intra-inter prediction

CPUs: Central Processing Units CRT: Cathode Ray Tube CTB: Coding TreeBlock CTBs: Coding Tree Blocks CTU: Coding Tree Unit CTUs: Coding TreeUnits CU: Coding Unit DMVR: Decoder-side Motion Vector Refinement DPB:Decoded Picture Buffer DPS: Decoding Parameter Set DVD: Digital VideoDisc FPGA: Field Programmable Gate Areas GBI: Generalized Bi-predictionGOPs: Groups of Pictures GPUs: Graphics Processing Units

GSM: Global System for Mobile communicationsHDR: high dynamic range

HEVC: High Efficiency Video Coding HRD: Hypothetical Reference DecoderIBC (or IntraBC): Intra Block Copy IC: Integrated Circuit ISP: IntraSub-Partitions

JEM: joint exploration model

JVET: Joint Video Exploration Team LAN: Local Area Network LCD:Liquid-Crystal Display LCU: Largest Coding Unit LR: Loop RestorationFilter LSO: Local Sample Offset LTE: Long-Term Evolution

MMVD: Merge Mode with Motion Vector DifferenceMPM: most probable mode

MV: Motion Vector MV: Motion Vector

MVD: Motion Vector differenceMVD: Motion vector difference

MVP: Motion Vector Predictor OLED: Organic Light-Emitting Diode PBs:Prediction Blocks PCI: Peripheral Component Interconnect PDPC: PositionDependent Prediction Combination PLD: Programmable Logic Device POC:Picture Order Count PPS: Picture Parameter Set PU: Prediction Unit PUs:Prediction Units RAM: Random Access Memory ROM: Read-Only Memory RPS:Reference Picture Set SAD: Sum of Absolute Difference SAO: SampleAdaptive Offset SB: Super Block SCC: Screen Content Coding SDP: SemiDecoupled Partitioning

SDR: standard dynamic range

SDT: Semi Decoupled Tree SEI: Supplementary Enhancement Information SNR:Signal Noise Ratio SPS: Sequence Parameter Setting

SSD: solid-state drive

SST: Semi Separate Tree TM: Template Matching TU: Transform Unit TUs:Transform Units, USB: Universal Serial Bus VPS: Video Parameter Set VUI:Video Usability Information

VVC: versatile video coding

WAIP: Wide-Angle Intra Prediction

What is claimed is:
 1. A method comprising: receiving a coded videostream comprising a syntax element indicating whether a sample offsetfiltering process is applied to a frame in the coded video stream at ablock level; determining that at least one of: a generalized sampleoffset (GSO), a local sample offset (LSO), or a cross component sampleoffset (CCSO) is enabled for the frame at the block level based on thesyntax element being a predefined value; and decoding the coded videostream by applying the at least one of the GSO, the LSO, or the CCSO atthe block level.
 2. The method of claim 1, wherein determining that theat least one of the GSO, the LSO, or the CCSO is enabled comprisesdetermining that the GSO is enabled based on the syntax element beingthe predefined value.
 3. The method of claim 1, wherein determining thatthe at least one of the GSO, the LSO, or the CCSO is enabled comprisesdetermining that the LSO is enabled based on the syntax element beingthe predefined value.
 4. The method of claim 1, wherein determining thatthe at least one of the GSO, the LSO, or the CCSO is enabled comprisesdetermining that the CCSO is enabled based on the syntax element beingthe predefined value.
 5. The method of claim 1, further comprising:receiving a signal indicating a first block-level flag for a lumacomponent having a first block size that is the same as or smaller thana second block size of a chroma component when a second block-level flagfor the chroma component having the second block size is signaled. 6.The method of claim 1, further comprising: receiving a block-level flagindicating that one of the GSO, the LSO, or the CCSO is enabled for ablock, wherein the block-level flag also indicates that another of theGSO, the LSO, or the CCSO is enabled for the block.
 7. The method ofclaim 1, further comprising: receiving, in a high-level syntax, a signalindicating a granularity of at least one of a chroma component or a lumacomponent for application of the GSO, wherein the high-level syntaxcomprises: a video parameter set (VPS), a picture parameter set (PPS), asequence parameter setting (SPS), an adaptation parameter set (APS), aframe header, a slice header, a picture header, a tile header, asuperblock header, or a coding tree unit (CTU) header.
 8. The method ofclaim 1, wherein the syntax element comprises a high-level syntax, theGSO enabled by the high-level syntax, the method further comprising:receiving a signal comprising an additional high-level syntax toindicate a maximum number of bands used for a band offset.
 9. The methodof claim 8, wherein the high-level syntax comprises: a video parameterset (VPS), a picture parameter set (PPS), a sequence parameter setting(SPS), an adaptation parameter set (APS), a frame header, a sliceheader, a picture header, a tile header, a superblock header, or acoding tree unit (CTU) header.
 10. The method of claim 1, wherein ablock-level flag enables the GSO for a block, the method furthercomprising: receiving a signal comprising an additional high-levelsyntax to indicate a number of bands used for a band offset in theblock.
 11. The method of claim 10, wherein the number of bands for theband offset in the block is less than a number of bands signaled at aframe level.
 12. The method of claim 10, wherein the syntax elementcomprises a high-level syntax, the method further comprising: receivinga signal comprising a flag to indicate whether a single band or amaximum number of bands specified in the high-level syntax is appliedfor a current block.
 13. The method of claim 1, wherein a block size ofthe frame in the coded video stream is different for a luma componentand a chroma component corresponding to the frame.
 14. An apparatus fordecoding a video stream, the apparatus comprising: a memory storing aplurality of instructions; and a processor configured to execute theplurality of instructions, and upon execution of the plurality ofinstructions, is configured to: receive a coded video stream comprisinga syntax element indicating whether a sample offset filtering process isapplied to a frame in the coded video stream at a block level; determinethat at least one of: a generalized sample offset (GSO), a local sampleoffset (LSO), or a cross component sample offset (CCSO) is enabled forthe frame at the block level based on the syntax element being apredefined value; and decode the coded video stream by application ofthe at least one of the GSO, the LSO, or the CCSO at the block level.15. The apparatus of claim 14, wherein application of the at least oneof the GSO, the LSO, or the CCSO comprises application of the GSO, andwherein a first block size of a luma component is the same as or smallerthan a second block size of the chroma component.
 16. The apparatus ofclaim 14, wherein the processor, upon execution of the plurality ofinstructions, is further configured to: receive a signal indicating afirst block-level flag for a luma component having a first block sizethat is the same as or smaller than a second block size of a chromacomponent when a second block-level flag for the chroma component havingthe second block size is signaled.
 17. The apparatus of claim 14,wherein the processor, upon execution of the plurality of instructions,is further configured to: receive a block-level flag indicating that oneof the GSO, the LSO, or the CCSO is enabled for a block, wherein theblock-level flag also indicates that another of the GSO, the LSO, or theCCSO is enabled for the block.
 18. The apparatus of claim 14, whereinthe processor, upon execution of the plurality of instructions, isfurther configured to receive, in a high-level syntax, a signalindicating a granularity of at least one of a chroma component or a lumacomponent for application of the GSO, wherein the high-level syntaxcomprises: a video parameter set (VPS), a picture parameter set (PPS), asequence parameter setting (SPS), an adaptation parameter set (APS), aframe header, a slice header, a picture header, a tile header, asuperblock header, or a coding tree unit (CTU) header.
 19. The apparatusof claim 14, wherein at least one of: the syntax element comprises ahigh-level syntax, the GSO is enabled by the high-level syntax, and theprocessor, upon execution of the plurality of instructions, is furtherconfigured to receive a signal comprising an additional high-levelsyntax to indicate a maximum number of bands used for a band offset; ora block-level flag enables the GSO for a block, and the processor, uponexecution of the plurality of instructions, is further configured to:receive a signal comprising an additional high-level syntax to indicatea number of bands used for a band offset in the block.
 20. Anon-transitory computer readable storage medium storing a plurality ofinstructions executable by a processor, wherein upon execution by theprocessor, the plurality of instructions is configured to cause theprocessor to: receive a coded video stream comprising a syntax elementindicating whether a sample offset filtering process is applied to aframe in the coded video stream at a block level; determine that atleast one of: a generalized sample offset (GSO), a local sample offset(LSO), or a cross component sample offset (CCSO) is enabled for theframe at the block level based on the syntax element being a predefinedvalue; and decode the coded video stream by application of the at leastone of the GSO, the LSO, or the CCSO at the block level.